Sample records for calreticulin transacetylase catalyzed

  1. Calreticulin transacetylase catalyzed activation of rat tracheal smooth muscle cell nitric oxide synthase by acetoxycoumarins.

    PubMed

    Arora, Shvetambri; Vohra, Parag; Kumar, Ajit; Tyagi, Yogesh Kumar; Raj, Hanumantharao Guru; Dawarkanath, Bilekere Srinivasarao; Saluja, Daman; Saso, Luciano; Parmar, Virinder Singh

    2008-04-01

    The Transacetylase function of Calreticulin (CR) catalyzing the transfer of acetyl groups from acetoxycoumarins (AC) to certain proteins was identified for the first time in our laboratory. Protein acetyltransferase action of CR was termed Calreticulin Transacetylase (CRTAase). In the present work, CRTAase of rat tracheal smooth muscle cells (TSMC) was characterized with respect to the specificity for various AC and its role in the activation of nitric oxide synthase (NOS). 7,8-Diacetoxy-4-methylcoumarin (DAMC), a model AC, when incubated with TSMC along with L-arginine caused profound activation of NOS as compared to that with L-arginine alone. Further, the inclusion of N-omega-nitro-L-arginine methyl ester (L-NAME) along with DAMC resulted in the reduction of NO levels of TSMC to that of control, there by confirming the activation of TSMC NOS. Also, several AC were found to activate TSMC NOS in tune with their specificities to CRTAase. The results presented in this paper bear evidence for the activation of TSMC NOS by AC and their effectiveness to enhance NO of airway cells may be expected to find useful applications in respiratory diseases. PMID:18379067

  2. Calreticulin transacetylase catalyzed modification of the TNF-? mediated pathway in the human peripheral blood mononuclear cells by polyphenolic acetates

    Microsoft Academic Search

    Usha Singh; Ajit Kumar; Rajesh Sinha; Sushma Manral; Shvetambri Arora; Sant Ram; Rakesh K. Mishra; Prachi Gupta; Surendra K. Bansal; Ashok K. Prasad; Shyam Biswal; Virinder S. Parmar; Hanumantharao G. Raj

    2010-01-01

    Polyphenols, coumarin (1,2-benzopyrone) and chromone (1,4-benzopyrone), are naturally occurring constituent of variety of plant species. They have attracted immense interest because of their diverse pharmacological activities. Not much was known about biological activities of acetyl derivative (polyphenolic acetates) of parent polyphenols. In previous investigations, we have conclusively established calreticulin transacetylase catalyzed activation of endothelial nitric oxide synthase (eNOS) by polyphenolic

  3. Characterization of protein transacetylase from human placenta as a signaling molecule calreticulin using polyphenolic peracetates as the acetyl group donors

    Microsoft Academic Search

    Seema; Ranju Kumari; Garima Gupta; Daman Saluja; Ajit Kumar; Sanjay Goel; Yogesh K. Tyagi; Ruchika Gulati; Anjali Vinocha; Kambadoor Muralidhar; Bilikere S. Dwarakanth; Ramesh C. Rastogi; Virinder S. Parmar; Shamkant A. Patkar; Hanumantharao G. Raj

    2007-01-01

    We have earlier shown that a unique membrane-bound enzyme mediates the transfer of acetyl group(s) from polyphenolic peracetates\\u000a (PA) to functional proteins, which was termed acetoxy drug: protein transacetylase (TAase) because it acted upon several classes\\u000a of PA. Here, we report the purification of TAase from human placentral microsomes to homogeneity with molecular mass of 60\\u000a kDa, exhibiting varying degrees

  4. Calreticulin Induces Dilated Cardiomyopathy

    PubMed Central

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

    2013-01-01

    Background Calreticulin, a Ca2+-buffering chaperone of the endoplasmic reticulum, is highly expressed in the embryonic heart and is essential for cardiac development. After birth, the calreticulin gene is sharply down regulated in the heart, and thus, adult hearts have negligible levels of calreticulin. In this study we tested the role of calreticulin in the adult heart. Methodology/Principal Findings We generated an inducible transgenic mouse in which calreticulin is targeted to the cardiac tissue using a Cre/loxP system and can be up-regulated in adult hearts. Echocardiography analysis of hearts from transgenic mice expressing calreticulin revealed impaired left ventricular systolic and diastolic function and impaired mitral valve function. There was altered expression of Ca2+ signaling molecules and the gap junction proteins, Connexin 43 and 45. Sarcoplasmic reticulum associated Ca2+-handling proteins (including the cardiac ryanodine receptor, sarco/endoplasmic reticulum Ca2+-ATPase, and cardiac calsequestrin) were down-regulated in the transgenic hearts with increased expression of calreticulin. Conclusions/Significance We show that in adult heart, up-regulated expression of calreticulin induces cardiomyopathy in vivo leading to heart failure. This is due to an alternation in changes in a subset of Ca2+ handling genes, gap junction components and left ventricle remodeling. PMID:23437120

  5. Calreticulin Mutations in Myeloproliferative Neoplasms

    PubMed Central

    Lavi, Noa

    2014-01-01

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

  6. Calreticulin mutations in myeloproliferative neoplasms.

    PubMed

    Lavi, Noa

    2014-10-01

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

  7. Acetoxy drug: protein transacetylase of buffalo liver-characterization and mass spectrometry of the acetylated protein product.

    PubMed

    Kohli, Ekta; Gaspari, Marco; Raj, Hanumantharao G; Parmar, Virinder S; Sharma, Sunil K; van der Greef, Jan; Kumari, Ranju; Gupta, Garima; Seema; Khurana, Pulkit; Tyagi, Yogesh K; Watterson, Arthur C; Olsen, Carl E

    2004-04-01

    The purification and characterization of the buffalo liver microsomal transacetylase (TAase) catalyzing the transfer of acetyl groups from a model acetoxy drug: 7,8-diacetoxy-4-methylcoumarin (DAMC) to GST3-3 has been described here. The enzyme was routinely assayed using DAMC and cytosolic GST as the substrates and was partially purified from microsomes of the buffalo liver. The enzyme was found to have approximate molecular of weight 65 kDa. The action of TAase and DAMC on liver cytosolic GST resulted in the formation of monoacetoxymonohydroxy-4-methylcoumarin (MAMHC) and 7,8-dihydroxy-4-methylcoumarin (DHMC), although the former was the major metabolite. The buffalo liver microsomal TAase exhibited hyperbolic kinetics and yielded K(m) (1667 microM) and V(max) (192 units) when the concentration of DAMC was varied keeping the concentration of GST constant. After having characterized the nature of the substrates and a product of the TAase-catalyzed reaction, we set out to identify the acetylated protein which is another product of the reaction. GST3-3 was used as a model protein substrate for the action of TAase using DAMC as the acetyl donor. The subunit of control and modified GST3-3 were separated by SDS-polyacrylamide gel electrophoresis (PAGE) and digested with trypsin. The tryptic peptides were extracted from the gel pieces and analyzed by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOFMS). The data search for calibrated and labeled mass peaks of peptides was performed on the Matrix Science Server using the search engine Mascot. The peptide maps so obtained covered 97% of the GST3-3 sequence. On comparison of MALDI peptide maps of modified and control GST, seven new peaks were recognized corresponding to the potentially acetylated peptides in peptide map. The mass value of each of them was 42 Da higher than the theoretical mass of a non-modified GST3-3 tryptic peptide, strongly suggesting acetylation. By examining the fragmentation patterns and by comparing experimental and predicted values for MS/MS daughter ions, the identity of the seven acetylated GST tryptic peptides could be confirmed by the application of LC/MS/MS. In the modified GST, N-terminal proline and six lysines (Lys(51), Lys(82), Lys(123), Lsy(181), Lys(191) and Lys(210)) were found to be acetylated. The structure of acetylated GST revealed that the lysines that underwent acetylation were peripheral in positions. PMID:15063315

  8. Calreticulin: Roles in Cell-Surface Protein Expression

    PubMed Central

    Jiang, Yue; Dey, Sandeepa; Matsunami, Hiroaki

    2014-01-01

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

  9. Distinct clinical characteristics of myeloproliferative neoplasms with calreticulin mutations

    PubMed Central

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

    2014-01-01

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

  10. Altered expression of calreticulin during the development of fibrosis.

    PubMed

    Kypreou, Katerina P; Kavvadas, Panagiotis; Karamessinis, Panagiotis; Peroulis, Michalis; Alberti, Avra; Sideras, Paschalis; Psarras, Stelios; Capetanaki, Yasemie; Politis, Panagiotis K; Charonis, Aristidis S

    2008-06-01

    Tissue damage following injury leads to inflammation and fibrosis. To understand the molecular mechanisms and the proteins involved in the fibrotic process, we used the well-established unilateral ureteric obstruction rat model and we analyzed the alterations at early and late time intervals using a classical proteomic approach. Data analysis demonstrates a correlation between calreticulin up-regulation and progression of fibrosis. Calreticulin is involved in Ca++ homeostasis but has not been previously implicated in animal models of fibrosis. Proteomic analysis consistently revealed up-regulation of calreticulin in both early and late time intervals. These findings were further confirmed by biochemical and morphological approaches. Next, animal models of lung fibrosis (bleomycin-induced) and heart fibrosis (desmin-null) were examined. In the lung model, calreticulin expression was up-regulated from early time intervals, whereas in the heart model no change in the expression of calreticulin was observed. In addition, TGF-beta, a well known major contributing factor in several fibrotic processes, was found to up-regulate calreticulin in cultured human proximal tubule epithelial cells. The above observations suggest that calreticulin might be involved in fibrotic processes; however the mechanism(s) underlying its possible involvement are yet unresolved. PMID:18563736

  11. 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

  12. 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

  13. CALRETICULIN IS ENRICHED IN THE CRYSTAL IDIOBLASTS OF PISTIA STRATIOTES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Calreticulin (CRT) has the highest calcium-binding capacity of the endoplasmic reticulum (ER) proteins found thus far in plants. In this study, we isolated cDNAs encoding CRT from Pistia stratiotes and analyzed the temporal and spatial patterns of CRT expression in leaves. Northern analysis showed...

  14. Comparison of protein acetyltransferase action of CRTAase with the prototypes of HAT.

    PubMed

    Ponnan, Prija; Kumar, Ajit; Singh, Prabhjot; Gupta, Prachi; Joshi, Rini; Gaspari, Marco; 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

  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. Release of calreticulin from neutrophils may alter C1q-mediated immune functions.

    PubMed Central

    Kishore, U; Sontheimer, R D; Sastry, K N; Zaner, K S; Zappi, E G; Hughes, G R; Khamashta, M A; Strong, P; Reid, K B; Eggleton, P

    1997-01-01

    Calreticulin is an abundant intracellular protein which is involved in a number of cellular functions. During cytomegalovirus infection, as well as inflammatory episodes in autoimmune disease, calreticulin can be released from cells and detected in the circulation, where it may act as an immunodominant autoantigen in diseases such as systemic lupus erythematosus. Calreticulin is known to bind to the molecules of innate immunity, such as C1q, the first subcomponent of complement. However, the functional implications of C1q-calreticulin interactions are unknown. In the present study we sought to investigate, in greater detail, the interaction between these two proteins following the release of calreticulin from neutrophils upon stimulation. In order to pinpoint the regions of interaction, recombinant calreticulin and its discrete domains (N-, P- and C-domains) were produced in Escherichia coli. Both the N- and P-domains of calreticulin were shown to bind to the globular head regions of C1q. Calreticulin also appeared to alter C1q-mediated immune functions. Binding of calreticulin to C1q inhibited haemolysis of IgM-sensitized erythrocytes. Both the N- and P-domains of calreticulin were found to contain sites involved in the inhibition of C1q-induced haemolysis. Full-length calreticulin, and its N- and P-domains, were also able to reduce the C1q-dependent binding of immune complexes to neutrophils. We conclude that calreticulin, once released from neutrophils during inflammation, may not only induce an antigenic reaction, but, under defined conditions, may also interfere with C1q-mediated inflammatory processes. PMID:9065775

  17. 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

  18. Nerve growth factor induces the expression of chaperone protein calreticulin in human epithelial ovarian cells.

    PubMed

    Vera, C; Tapia, V; Kohan, K; Gabler, F; Ferreira, A; Selman, A; Vega, M; Romero, C

    2012-07-01

    Epithelial ovarian cancer is highly angiogenic and high expression of Nerve Growth Factor (NGF), a proangiogenic protein. Calreticulin is a multifunctional protein with anti-angiogenic properties and its translocation to the tumor cell membrane promotes recognition and engulfment by dendritic cells. The aim of this work was to evaluate calreticulin expression in human normal ovaries, benign and borderline tumors, and epithelial ovarian cancer samples and to evaluate whether NGF regulates calreticulin expression in human ovarian surface epithelium and in epithelial ovarian cancer cell lines. Calreticulin mRNA and protein levels were analyzed using RT-PCR, Western blot and immunohistochemistry in 67 human ovarian samples obtained from our Institution. Calreticulin expression induced by NGF stimulation in cell lines was evaluated using RT-PCR, Western blot and immunocytochemistry. We found a significant increase of calreticulin mRNA levels in epithelial ovarian cancer samples as compared to normal ovaries, benign tumors, and borderline tumors. Calreticulin protein levels, evaluated by Western blot, were also increased in epithelial ovarian cancer with respect to benign and borderline tumors. When HOSE and A2780 cell lines were stimulated with Nerve Growth Factor, we found an increase in calreticulin protein levels compared to controls. This effect was reverted by GW441756, a TRKA specific inhibitor. These results suggest that NGF regulates calreticulin protein levels in epithelial ovarian cells through TRKA receptor activation. PMID:22773372

  19. The evolutionary history of calreticulin and calnexin genes in green plants.

    PubMed

    Del Bem, Luiz Eduardo V

    2011-02-01

    Calreticulin and calnexin are Ca(2+)-binding chaperones localized in the endoplasmic reticulum of eukaryotes acting in glycoprotein folding quality control and Ca(2+) homeostasis. The evolutionary histories of calreticulin and calnexin gene families were inferred by comprehensive phylogenetic analyses using 18 completed genomes and ESTs covering the major green plants groups, from green algae to angiosperms. Calreticulin and calnexin possibly share a common origin, and both proteins are present along all green plants lineages. The calreticulin founder gene within green plants duplicated in early tracheophytes leading to two possible groups of orthologs with specialized functions, followed by lineage-specific gene duplications in spermatophytes. Calnexin founder gene in land plants was inherited from basal green algae during evolution in a very conservative copy number. A comprehensive classification in possible groups of orthologs and a catalog of calreticulin and calnexin genes from green plants are provided. PMID:21222018

  20. Substrate Specificity of the Oxidoreductase ERp57 Is Determined Primarily by Its Interaction with Calnexin and Calreticulin*

    PubMed Central

    Jessop, Catherine E.; Tavender, Timothy J.; Watkins, Rachel H.; Chambers, Joseph E.; Bulleid, Neil J.

    2009-01-01

    The formation of disulfides within proteins entering the secretory pathway is catalyzed by the protein disulfide isomerase family of endoplasmic reticulum localized oxidoreductases. One such enzyme, ERp57, is thought to catalyze the isomerization of non-native disulfide bonds formed in glycoproteins with unstructured disulfide-rich domains. Here we investigated the mechanism underlying ERp57 specificity toward glycoprotein substrates and the interdependence of ERp57 and the calnexin cycle for their correct folding. Our results clearly show that ERp57 must be physically associated with the calnexin cycle to catalyze isomerization reactions with most of its substrates. In addition, some glycoproteins only require ERp57 for correct disulfide formation if they enter the calnexin cycle. Hence, the specificity of ER oxidoreductases is not only determined by the physical association of enzyme and substrate but also by accessory factors, such as calnexin and calreticulin in the case of ERp57. These conclusions suggest that the calnexin cycle has evolved with a specialized oxidoreductase to facilitate native disulfide formation in complex glycoproteins. PMID:19054761

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

    PubMed

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

    2014-09-01

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

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

    PubMed Central

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

    2014-01-01

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

  3. 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

  4. Unfolded protein response suppresses CEBPA by induction of calreticulin in acute myeloid leukaemia.

    PubMed

    Schardt, Julian A; Eyholzer, Marianne; Timchenko, Nikolai A; Mueller, Beatrice U; Pabst, Thomas

    2010-06-01

    The unfolded protein response (UPR) is triggered by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). The role of the UPR during leukemogenesis is unknown so far. Here, we studied the induction of mediators of the UPR in leukaemic cells of AML patients. Increased expression of the spliced variant of the X-box binding protein 1 (XBP1s) was detected in 17.4% (16 of 92) of AML patients. Consistent with activated UPR, this group also had increased expression of ER-resident chaperones such as the 78 kD glucose-regulated protein (GRP78) and of calreticulin. Conditional expression of calreticulin in leukaemic U937 cells was found to increase calreticulin binding to the CEBPA mRNA thereby efficiently blocking translation of the myeloid key transcription factor CEBPA and ultimately affecting myeloid differentiation. Consequently, leukaemic cells from AML patients with activated UPR and thus increased calreticulin levels showed in fact suppressed CEBPA protein expression. We identified two functional ER stress response elements (ERSE) in the calreticulin promoter. The presence of NFY and ATF6, as well as an intact binding site for YY1 within these ERSE motifs were essential for mediating sensitivity to ER stress and activation of calreticulin. Thus, we propose a model of the UPR being activated in a considerable subset of AML patients through induction of calreticulin along the ATF6 pathway, thereby ultimately suppressing CEBPA translation and contributing to the block in myeloid differentiation. PMID:19659458

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

    PubMed

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

    2011-06-01

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

  6. 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

  7. Entamoeba histolytica Cell Surface Calreticulin Binds Human C1q and Functions in Amebic Phagocytosis of Host Cells

    PubMed Central

    Vaithilingam, Archana; Teixeira, Jose E.; Miller, Peter J.; Heron, Bradley T.

    2012-01-01

    Phagocytosis of host cells is characteristic of tissue invasion by the intestinal ameba Entamoeba histolytica, which causes amebic dysentery and liver abscesses. Entamoeba histolytica induces host cell apoptosis and uses ligands, including C1q, on apoptotic cells to engulf them. Two mass spectrometry analyses identified calreticulin in amebic phagosome preparations, and, in addition to its function as an endoplasmic reticulum chaperone, calreticulin is believed to be the macrophage receptor for C1q. The purpose of this study was to determine if calreticulin functions as an E. histolytica C1q receptor during phagocytosis of host cells. Calreticulin was localized to the surface of E. histolytica during interaction with both Jurkat lymphocytes and erythrocytes and was present in over 75% of phagocytic cups during amebic erythrophagocytosis. Presence of calreticulin on the cell surface was further demonstrated using a method that selectively biotinylated cell surface proteins and by flow cytometry using trophozoites overexpressing epitope-tagged calreticulin. Regulated overexpression of calreticulin increased E. histolytica's ability to phagocytose apoptotic lymphocytes and calcium ionophore-treated erythrocytes but had no effect on amebic adherence to or destruction of cell monolayers or surface expression of the GalNAc lectin and serine-rich E. histolytica protein (SREHP) receptors. Finally, E. histolytica calreticulin bound specifically to apoptotic lymphocytes and to human C1q. Collectively, these data implicate cell surface calreticulin as a receptor for C1q during E. histolytica phagocytosis of host cells. PMID:22473608

  8. Roles for Calreticulin and a Novel Glycoprotein, Tapasin, in the Interaction of MHC Class I Molecules with TAP

    Microsoft Academic Search

    Bhanu Sadasivan; Paul J Lehner; Bodo Ortmann; Thomas Spies; Peter Cresswell

    1996-01-01

    Assembly of MHC class I–?2 microglobulin (?2m) dimers in the endoplasmic reticulum involves two chaperones. Calnexin has previously been shown to interact with free class I heavy chains. Here, we show that the related chaperone, calreticulin, binds human class I–?2m dimers prior to peptide loading. Calreticulin remains associated with at least a subset of class I molecules when they, in

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

    PubMed Central

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

    2002-01-01

    Protein-protein interactions play an important role in the regulation of enzymic activity of pyruvate dehydrogenase kinase (PDK). It is generally believed that the binding of PDK to the inner lipoyl-bearing domain L2 of the transacetylase component E2 of pyruvate dehydrogenase complex largely determines the level of kinase activity. In the present study, we characterized the interaction between the individual isoenzymes of PDK (PDK1-PDK4) and monomeric L2 domain of human E2, as well as the effect of this interaction on kinase activity. It was found that PDK isoenzymes are markedly different with respect to their affinities for L2. PDK3 demonstrated a very tight binding, which persisted during isolation of PDK3-L2 complexes using size-exclusion chromatography. Binding of PDK1 and PDK2 was readily reversible with the apparent dissociation constant of approx. 10 microM for both isoenzymes. PDK4 had a greatly reduced capacity for L2 binding (relative order PDK3>PDK1=PDK2>PDK4). Monomeric L2 domain alone had very little effect on the activities of either PDK1 or PDK2. In contrast, L2 caused a 3-fold increase in PDK3 activity and approx. 37% increase in PDK4 activity. These results strongly suggest that the interactions between the individual isoenzymes of PDK and L2 domain are isoenzyme-specific and might be among the major factors that determine the level of kinase activity of particular isoenzyme towards the pyruvate dehydrogenase complex. PMID:11978179

  10. Recognition of the Inner Lipoyl-Bearing Domain of Dihydrolipoyl Transacetylase and of the Blood Glucose-Lowering Compound AZD7545 by Pyruvate Dehydrogenase Kinase 2†

    PubMed Central

    Tuganova, Alina; Klyuyeva, Alla; Popov, Kirill M.

    2007-01-01

    Pyruvate dehydrogenase kinase 2 (PDHK2) is a unique mitochondrial protein kinase that regulates the activity of the pyruvate dehydrogenase multienzyme complex (PDC). PDHK2 is an integral component of PDC tightly bound to the inner lipoyl-bearing domains (L2) of the dihydrolipoyl transacetylase component (E2) of PDC. This association has been reported to bring about an up to 10-fold increase in kinase activity. Despite the central role played by E2 in the maintenance of PDHK2 functionality in the PDC-bound state, the molecular mechanisms responsible for the recognition of L2 by PDHK2 and for the E2-dependent PDHK2 activation are largely unknown. In this study, we used a combination of molecular modeling and site-directed mutagenesis to identify the amino acid residues essential for the interaction between PDHK2 and L2 and for the activation of PDHK2 by E2. On the basis of the results of site-directed mutagenesis, it appears that a number of PDHK2 residues located in its R domain (P22, L23, F28, F31, F44, L45, and L160) and in the so-called “cross arm” structure (K368, R372, and K391) are critical in determining the strength of the interaction between PDHK2 and L2. The residues of L2 essential for recognition by PDHK2 include L140, K173, I176, E179, and to a lesser extent D164, D172, and A174. Importantly, certain PDHK2 residues forming interfaces with L2, i.e., K17, P22, F31, F44, R372, and K391, are also critical for the maintenance of enhanced PDHK2 activity in the E2-bound state. Finally, evidence that the blood glucose-lowering compound AZD7545 disrupts the interactions between PDHK2 and L2 and thereby inhibits PDHK2 activity is presented. PMID:17602666

  11. Presence of calreticulin mutations in JAK2-negative polycythemia vera.

    PubMed

    Broséus, Julien; Park, Ji-Hye; Carillo, Serge; Hermouet, Sylvie; Girodon, François

    2014-12-18

    Calreticulin (CALR) mutations have been reported in Janus kinase 2 (JAK2)- and myeloproliferative leukemia (MPL)-negative essential thrombocythemia and primary myelofibrosis. In contrast, no CALR mutations have ever been reported in the context of polycythemia vera (PV). Here, we describe 2 JAK2(V617F)-JAK2(exon12)-negative PV patients who presented with a CALR mutation in peripheral granulocytes at the time of diagnosis. In both cases, the CALR mutation was a 52-bp deletion. Single burst-forming units-erythroid (BFU-E) from 1 patient were grown in vitro and genotyped: the same CALR del 52-bp mutation was noted in 31 of the 37 colonies examined; 30 of 31 BFU-E were heterozygous for CALR del 52 bp, and 1 of 31 BFU-E was homozygous for CALR del 52 bp. In summary, although unknown mutations leading to PV cannot be ruled out, our results suggest that CALR mutations can be associated with JAK2-negative PV. PMID:25305205

  12. Immunological Activity Difference between Native Calreticulin Monomers and Oligomers

    PubMed Central

    He, Mi-chun; Wang, Jun; Wu, Jian; Gong, Fang-yuan; Hong, Chao; Xia, Yun; Zhang, Li-juan; Bao, Wan-rong; Gao, Xiao-Ming

    2014-01-01

    We have recently demonstrated that the greatly increased immunological activities of recombinant murine calreticulin (rCRT) are largely attributed to its self-oligomerization. Although native CRT (nCRT) can also oligomerize under stress conditions in vitro, whether this phenomenon could occur inside cells and the immunological activity difference between nCRT monomers and oligomers remained unclear. In this study, we illustrated the formation of CRT oligomers in tranfectant cells under “heat & low pH” (42°C/pH 6.5) condition. The mixture of nCRT oligomers and monomers (OnCRT) was obtained after 3 hr treatment of murine monomeric nCRT (MnCRT) under similar condition (42°C/pH 5.0) in vitro. The OnCRT thus obtained was better recognized by 2 monoclonal Abs from mice that had been immunized with oligomeric rCRT. Unlike MnCRT, OnCRT was able to elicit CRT-specific IgG production in mice. OnCRT also stimulated bone-marrow derived dendritic cells (BMDCs) to secrete significantly higher levels of TNF-?, IL-6 and IL-12p40 than did MnCRT in vitro. We postulate that oligomerization of soluble CRT may occur under certain pathophysiological conditions (e.g. ultrahyperpyrexia) and the resultant oligomers may exhibit exaggerated immunostimulating activities, thereby affiliating the inflammatory responses in vivo. PMID:25171171

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

    PubMed Central

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

    2000-01-01

    The engagement of integrin ?7 in E63 skeletal muscle cells by laminin or anti-?7 antibodies triggered transient elevations in the intracellular free Ca2+ concentration that resulted from both inositol triphosphate-evoked Ca2+ release from intracellular stores and extracellular Ca2+ influx through voltage-gated, L-type Ca2+ channels. The extracellular domain of integrin ?7 was found to associate with both ectocalreticulin and dihydropyridine receptor on the cell surface. Calreticulin appears to also associate with cytoplasmic domain of integrin ?7 in a manner highly dependent on the cytosolic Ca2+ concentration. It appeared that intracellular Ca2+ release was a prerequisite for Ca2+ influx and that calreticulin associated with the integrin cytoplasmic domain mediated the coupling of between the Ca2+ release and Ca2+ influx. These findings suggest that calreticulin serves as a cytosolic activator of integrin and a signal transducer between integrins and Ca2+ channels on the cell surface. PMID:10749940

  14. Thrombospondin 1 binding to calreticulin-LRP1 signals resistance to anoikis

    PubMed Central

    Pallero, Manuel A.; Elzie, Carrie A.; Chen, Jiping; Mosher, Deane F.; Murphy-Ullrich, Joanne E.

    2008-01-01

    Anoikis, apoptotic cell death due to loss of cell adhesion, is critical for regulation of tissue homeostasis in tissue remodeling. Fibrogenesis is associated with reduced fibroblast apoptosis. The matricellular protein thrombospondin 1 (TSP1) regulates cell adhesion and motility during tissue remodeling and in fibrogenesis. The N-terminal domain of TSP1 binds to the calreticulin-LRP1 receptor co-complex to signal down-regulation of cell adhesion and increased cell motility through focal adhesion disassembly. TSP1 signaling through calreticulin-LRP1 activates cell survival signals such as PI3-kinase. Therefore, we tested the hypothesis that TSP1 supports cell survival under adhesion-independent conditions to facilitate tissue remodeling. Here, we show that platelet TSP1, its N-terminal domain (NoC1) as a recombinant protein, or a peptide comprising the calreticulin-LRP1 binding site [amino acids 17–35 (hep I)] in the N-terminal domain promotes fibroblast survival under anchorage-independent conditions. TSP1 activates Akt and decreases apoptotic signaling through caspase 3 and PARP1 in suspended fibroblasts. Inhibition of PI3K/Akt activity blocks TSP1-mediated anchorage-independent survival. Fibroblasts lacking LRP1 or expressing calreticulin lacking the TSP1 binding site do not respond to TSP1 with anchorage-independent survival. These data define a novel role for TSP1 signaling through the calreticulin/LRP1 co-complex in tissue remodeling and fibrotic responses through stimulation of anoikis resistance.—Pallero, M. A., Elzie, C. A., Chen, J., Mosher, D. F., Murphy-Ullrich, J. E. Thrombospondin 1 binding to calreticulin-LRP1 signals resistance to anoikis. PMID:18653767

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

    PubMed

    Dey, Sandeepa; Matsunami, Hiroaki

    2011-10-01

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

  16. Calreticulin mutations and long-term survival in essential thrombocythemia.

    PubMed

    Tefferi, A; Wassie, E A; Lasho, T L; Finke, C; Belachew, A A; Ketterling, R P; Hanson, C A; Pardanani, A; Gangat, N; Wolanskyj, A P

    2014-12-01

    The impact of calreticulin (CALR) mutations on long-term survival in essential thrombocythemia (ET) was examined in 299 patients whose diagnosis predated 2006. Mutational frequencies were 53% for Janus kinase 2 (JAK2), 32% for CALR and 3% for MPL; the remaining 12% were 'triple-negative'. We confirmed the association of mutant CALR (vs JAK2V617F) with younger age (P=0.002), male sex (P=0.01), higher platelet count (0.0004), lower hemoglobin (P<0.0001), lower leukocyte count (0.02) and lower incidence of recurrent thrombosis (0.04). Triple-negative patients were also younger than their JAK2-mutated counterparts (P=0.003) and displayed lower hemoglobin (P=0.003), lower leukocyte count (<0.0001) and lower thrombotic events (P=0.02). Median follow-up time was 12.7 years and 47% of the patients were followed until death. Survival was the longest for triple-negative and shortest for MPL-mutated patients. Median survival was 19 years for JAK2 and 20 years for CALR-mutated cases (P=0.32); the corresponding figures for patients of age ?65 years were 26 and 32 years (P=0.56). The two mutational categories were also similar for leukemic (P=0.28) and fibrotic (P=0.28) progression rates. The current study is uniquely characterized by its very long follow-up period and provides accurate estimates of long-term survival in ET and complements current information on mutation-specific phenotype and prognosis. PMID:24791854

  17. Citrullinated calreticulin potentiates rheumatoid arthritis shared epitope signaling

    PubMed Central

    Ling, Song; Cline, Erika N; Haug, Timothy S; Fox, David A; Holoshitz, Joseph

    2012-01-01

    Objective Citrullinated proteins are immunogenic in rheumatoid arthritis (RA), particularly in patients that carry shared epitope (SE)-coding HLA-DRB1 alleles. The mechanism underlying this association is unknown. We have previously identified SE as a ligand that interacts with cell surface calreticulin (CRT) and activates immune dysregulation. The objective of this study was to determine the effect of CRT citrullination on SE signaling. Methods CRT-SE binding affinity was measured by surface plasmon resonance. The role of individual CRT arginine residues was determined by site-directed mutagenesis. Nitric oxide levels were measured using a fluorochrome-based assay. CRT citrullination in synovial tissues and cell cultures was determined by 2-dimensional gel electrophoresis, immunoblotting and mass spectrometry techniques. Results Synovial tissues and fibroblast-like synoviocytes from RA patients were found to express higher abundance of citrullinated CRT compared to OA samples. Citrullinated CRT showed more robust interaction with the SE ligand, and transduced SE signaling at a 10,000-fold higher potency, compared to non-citrullinated CRT. Site-directed mutation analysis identified Arg205, which is spatially adjacent to the SE binding site in the CRT P-domain, as a dominant inhibitor of SE-CRT interaction and signaling, while a more remote arginine residue, Arg261 was found to enhance these SE functions. Conclusion Citrullinated CRT is over-abundant in the RA synovium, and potentiates SE-activated signaling in vitro. These findings could introduce a new mechanistic model of gene-environment interaction in RA. PMID:23233327

  18. Calreticulin binds to gentamicin and reduces drug-induced ototoxicity.

    PubMed

    Karasawa, Takatoshi; Wang, Qi; David, Larry L; Steyger, Peter S

    2011-12-01

    Aminoglycosides like gentamicin are among the most commonly used antibiotics in clinical practice and are essential for treating life-threatening tuberculosis and Gram-negative bacterial infections. However, aminoglycosides are also nephrotoxic and ototoxic. Although a number of mechanisms have been proposed, it is still unclear how aminoglycosides induce cell death in auditory sensory epithelia and subsequent deafness. Aminoglycosides bind to various intracellular molecules, such as RNA and phosphoinositides. We hypothesized that aminoglycosides, based on their tissue-specific susceptibility, also bind to intracellular proteins that play a role in drug-induced ototoxicity. By conjugating an aminoglycoside, gentamicin, to agarose beads and conducting a gentamicin-agarose pull-down assay, we have isolated gentamicin-binding proteins (GBPs) from immortalized cells of mouse organ of Corti, HEI-OC1. Mass spectrometry identified calreticulin (CRT) as a GBP. Immunofluorescence revealed that CRT expression is concentrated in strial marginal cells and hair cell stereocilia, primary locations of drug uptake and cytotoxicity in the cochlea. In HEI-OC1 cells treated with gentamicin, reduction of CRT expression using small interfering RNA (siRNA) reduced intracellular drug levels. CRT-deficient mouse embryonic fibroblast (MEF) cells as well as CRT siRNA-transfected wild-type MEFs also had reduced cell viability after gentamicin treatment. A pull-down assay using deletion mutants of CRT determined that the carboxyl C-domain of CRT binds to gentamicin. HeLa cells transfected with CRT C-domain deletion mutant construct were more susceptible to gentamicin-induced cytotoxicity compared with cells transfected with full-length CRT or other deletion mutants. Therefore, we conclude that CRT binding to gentamicin is protective against gentamicin-induced cytotoxicity. PMID:21785162

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

    PubMed Central

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

    2013-01-01

    Endoplasmic reticulum (ER) stress is an emerging factor in fibrotic disease, although precise mechanisms are not clear. Calreticulin (CRT) is an ER chaperone and regulator of Ca2+ signaling up-regulated by ER stress and in fibrotic tissues. Previously, we showed that ER CRT regulates type I collagen transcript, trafficking, secretion, and processing into the extracellular matrix (ECM). To determine the role of CRT in ECM regulation under fibrotic conditions, we asked whether CRT modified cellular responses to the pro-fibrotic cytokine, TGF-?. These studies show that CRT?/? mouse embryonic fibroblasts (MEFs) and rat and human idiopathic pulmonary fibrosis lung fibroblasts with siRNA CRT knockdown had impaired TGF-? stimulation of type I collagen and fibronectin. In contrast, fibroblasts with increased CRT expression had enhanced responses to TGF-?. The lack of CRT does not impact canonical TGF-? signaling as TGF-? was able to stimulate Smad reporter activity in CRT?/? MEFs. CRT regulation of TGF-?-stimulated Ca2+ signaling is important for induction of ECM. CRT?/? MEFs failed to increase intracellular Ca2+ levels in response to TGF-?. NFAT activity is required for ECM stimulation by TGF-?. In CRT?/? MEFs, TGF-? stimulation of NFAT nuclear translocation and reporter activity is impaired. Importantly, CRT is required for TGF-? stimulation of ECM under conditions of ER stress, as tunicamycin-induced ER stress was insufficient to induce ECM production in TGF-? stimulated CRT?/? MEFs. Together, these data identify CRT-regulated Ca2+-dependent pathways as a critical molecular link between ER stress and TGF-? fibrotic signaling. PMID:23564462

  20. Molecular characterization of calreticulin from Anopheles stephensi midgut cells and functional assay of the recombinant calreticulin with Plasmodium berghei ookinetes.

    PubMed

    Borhani Dizaji, Nahid; Basseri, Hamid Reza; Naddaf, Saied Reza; Heidari, Mansour

    2014-10-25

    Transmission blocking vaccines (TBVs) that target the antigens on the midgut epithelium of Anopheles mosquitoes are among the promising tools for the elimination of the malaria parasite. Characterization and analysis of effective antigens is the first step to design TBVs. Calreticulin (CRT), a lectin-like protein, from Anopheles albimanus midgut, has shown antigenic features, suggesting a promising and novel TBV target. CRT is a highly conserved protein with similar features in vertebrates and invertebrates including anopheline. We cloned the full-length crt gene from malaria vector, Anopheles stephensi (AsCrt) and explored the interaction of recombinant AsCrt protein, expressed in a prokaryotic system (pGEX-6p-1), with surface proteins of Plasmodium berghei ookinetes by immunofluorescence assay. The cellular localization of AsCrt was determined using the baculovirus expression system. Sequence analysis of the whole cDNA of AsCrt revealed that AsCrt contains an ORF of 1221 bp. The amino acid sequence of AsCrt protein obtained in this study showed 64% homology with similar protein in human. The AsCrt shares the most common features of CRTs from other species. This gene encodes a 406 amino-acid protein with a molecular mass of 46 kDa, which contains a predicted 16 amino-acid signal peptides, conserved cysteine residues, a proline-rich region, and highly acidic C-terminal domain with endoplasmic reticulum retrieval sequence HDEL. The production of GST-AsCrt recombinant protein was confirmed by Western blot analysis using an antibody against the GST protein. The FITC-labeled GST-AsCrt exhibited a significant interaction with P. berghei ookinete surface proteins. Purified recombinant GST-AsCrt, labeled with FITC, displayed specific binding to the surface of P. berghei ookinetes in comparison with control. Moreover, the expression of AsCrt in baculovirus expression system indicated that AsCrt was localized on the surface of Sf9 cells. Our results suggest that AsCrt could be utilized as a potential target for future studies in TBV area for malaria control. PMID:25150160

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

    Microsoft Academic Search

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

    2005-01-01

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

  2. Macrophages eat cancer cells using their own calreticulin as a guide: Roles of TLR and Btk

    PubMed Central

    Feng, Mingye; Chen, James Y.; Weissman-Tsukamoto, Rachel; Volkmer, Jens-Peter; Ho, Po Yi; McKenna, Kelly M.; Cheshier, Samuel; Zhang, Michael; Guo, Nan; Gip, Phung; Mitra, Siddhartha S.; Weissman, Irving L.

    2015-01-01

    Macrophage-mediated programmed cell removal (PrCR) is an important mechanism of eliminating diseased and damaged cells before programmed cell death. The induction of PrCR by eat-me signals on tumor cells is countered by don’t-eat-me signals such as CD47, which binds macrophage signal-regulatory protein ? to inhibit phagocytosis. Blockade of CD47 on tumor cells leads to phagocytosis by macrophages. Here we demonstrate that the activation of Toll-like receptor (TLR) signaling pathways in macrophages synergizes with blocking CD47 on tumor cells to enhance PrCR. Bruton’s tyrosine kinase (Btk) mediates TLR signaling in macrophages. Calreticulin, previously shown to be an eat-me signal on cancer cells, is activated in macrophages for secretion and cell-surface exposure by TLR and Btk to target cancer cells for phagocytosis, even if the cancer cells themselves do not express calreticulin. PMID:25646432

  3. 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

  4. ldentification and Characterization of cDNA Clones Encoding Plant Calreticulin in Barley

    Microsoft Academic Search

    Fuqiang Chen; Patrick M. Hayes; Donna M. Mulrooney; Aihong Pan

    Two cDNA clones (CRH1 and CRH2) homologous to animal calreticulin, a major calcium storage protein in the lumen of the endoplasmic reticulum, were isolated from an ovary cDNA library of barley through differential screening. The two clones differ in the 3' untranslated region and the 5' region that encodes a putative N-terminal signal sequence. CRHl was mapped to the minus

  5. Identification and characterization of cDNA clones encoding plant calreticulin in barley.

    PubMed Central

    Chen, F; Hayes, P M; Mulrooney, D M; Pan, A

    1994-01-01

    Two cDNA clones (CRH1 and CRH2) homologous to animal calreticulin, a major calcium storage protein in the lumen of the endoplasmic reticulum, were isolated from an ovary cDNA library of barley through differential screening. The two clones differ in the 3' untranslated region and the 5' region that encodes a putative N-terminal signal sequence. CRH1 was mapped to the minus arm of chromosome 1. CRH2 was mapped to the minus arm of chromosome 2. The deduced amino acid sequences share 50 to 55% identity with animal calreticulins and exhibit the same three-zone characteristic. Recombinant protein stained blue with Stains-all and bound 45Ca2+ when transferred to nitrocellulose membranes. A native protein of approximately 55 kD was identified in ovary extract. Elevated gene expression was observed in ovaries 1 day after pollination and during early embryogenesis. CRH1 was expressed at a higher level than CRH2. These studies demonstrate the presence of calreticulin in plant cells and its developmental regulation in fertilization. PMID:7914763

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

    PubMed Central

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

    2002-01-01

    A robust mathematical model developed from single cell calcium (Ca(2+)) dynamics has enabled us to predict the consequences of over-expression of endoplasmic reticulum-located chaperones. Model predictions concluded that calreticulin interacts with the lumenal domain of the sarcoplasmic and endoplasmic reticulum Ca(2+)-activated ATPase (SERCA) pump, altering pump affinity for Ca(2+) (K(1/2) switches from 247 to 431 nM) and hence generating Ca(2+) oscillations. Expression of calreticulin in the ER generated an average of six transient-decline oscillations during the Ca(2+) recovery phase, upon exposure to maximal levels of the agonist ATP. In contrast, normal cells produced a single Ca(2+) transient with few or no oscillations. By conditioning the model to experimental data, parameters for generation and decay of IP(3) and SERCA pump kinetics were determined. To elucidate the possible source of the oscillatory behavior three possible oscillators, 1) IP(3), 2) IP(3)R, and 3) SERCA pump, were investigated and parameters constrained by experimental data to produce the best candidate. Each of the three oscillators generated very good fits with experimental data. However, converting a normal exponential recovery to a transient-decline oscillator predicted that the SERCA pump is the most likely candidate for calreticulin-mediated Ca(2+) release, highlighting the role of this chaperone as a signal protein within the endoplasmic reticulum. PMID:11806903

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

    PubMed

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

    2015-02-01

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

  8. Promotion of transferrin folding by cyclic interactions with calnexin and calreticulin.

    PubMed Central

    Wada, I; Kai, M; Imai, S; Sakane, F; Kanoh, H

    1997-01-01

    Calnexin, an abundant membrane protein, and its lumenal homolog calreticulin interact with nascent proteins in the endoplasmic reticulum. Because they have an affinity for monoglucosylated N-linked oligosaccharides which can be regenerated from the aglucosylated sugar, it has been speculated that this repeated oligosaccharide binding may play a role in nascent chain folding. To investigate the process, we have developed a novel assay system using microsomes freshly prepared from pulse labeled HepG2 cells. Unlike the previously described oxidative folding systems which required rabbit reticulocyte lysates, the oxidative folding of transferrin in isolated microsomes could be carried out in a defined solution. In this system, addition of a glucose donor, UDP-glucose, to the microsomes triggered glucosylation of transferrin and resulted in its cyclic interaction with calnexin and calreticulin. When the folding of transferrin in microsomes was analyzed, UDP-glucose enhanced the amount of folded transferrin and reduced the disulfide-linked aggregates. Analysis of transferrin folding in briefly heat-treated microsomes revealed that UDP-glucose was also effective in elimination of heat-induced misfolding. Incubation of the microsomes with an alpha-glucosidase inhibitor, castanospermine, prolonged the association of transferrin with the chaperones and prevented completion of folding and, importantly, aggregate formation, particularly in the calnexin complex. Accordingly, we demonstrate that repeated binding of the chaperones to the glucose of the transferrin sugar moiety prevents and corrects misfolding of the protein. PMID:9312001

  9. 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

  10. 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

  11. From Janus kinase 2 to calreticulin: the clinically relevant genomic landscape of myeloproliferative neoplasms.

    PubMed

    Cazzola, Mario; Kralovics, Robert

    2014-06-12

    Our understanding of the genetic basis of myeloproliferative neoplasms began in 2005, when the JAK2 (V617F) mutation was identified in polycythemia vera, essential thrombocythemia, and primary myelofibrosis. JAK2 exon 12 and MPL exon 10 mutations were then detected in subsets of patients, and subclonal driver mutations in other genes were found to be associated with disease progression. Recently, somatic mutations in the gene CALR, encoding calreticulin, have been found in most patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 and MPL. The JAK-STAT pathway appears to be activated in all myeloproliferative neoplasms, regardless of founding driver mutations. These latter, however, have different effects on clinical course and outcomes. Thus, evaluation of JAK2, MPL, and CALR mutation status is important not only for diagnosis but also for prognostication. These genetic data should now also be considered in designing clinical trials. PMID:24786775

  12. Cytokine, Antibody and Proliferative Cellular Responses Elicited by Taenia solium Calreticulin upon Experimental Infection in Hamsters

    PubMed Central

    Mendlovic, Fela; Cruz-Rivera, Mayra; Ávila, Guillermina; Vaughan, Gilberto; Flisser, Ana

    2015-01-01

    Taenia solium causes two diseases in humans, cysticercosis and taeniosis. Tapeworm carriers are the main risk factor for neurocysticercosis. Limited information is available about the immune response elicited by the adult parasite, particularly the induction of Th2 responses, frequently associated to helminth infections. Calreticulin is a ubiquitous, multifunctional protein involved in cellular calcium homeostasis, which has been suggested to play a role in the regulation of immune responses. In this work, we assessed the effect of recombinant T. solium calreticulin (rTsCRT) on the cytokine, humoral and cellular responses upon experimental infection in Syrian Golden hamsters (Mesocricetus auratus). Animals were infected with T. solium cysticerci and euthanized at different times after infection. Specific serum antibodies, proliferative responses in mesenteric lymph nodes and spleen cells, as well as cytokines messenger RNA (mRNA) were analyzed. The results showed that one third of the infected animals elicited anti-rTsCRT IgG antibodies. Interestingly, mesenteric lymph node (MLN) cells from either infected or non-infected animals did not proliferate upon in vitro stimulation with rTsCRT. Additionally, stimulation with a tapeworm crude extract resulted in increased expression of IL-4 and IL-5 mRNA. Upon stimulation, rTsCRT increased the expression levels of IL-10 in spleen and MLN cells from uninfected and infected hamsters. The results showed that rTsCRT favors a Th2-biased immune response characterized by the induction of IL-10 in mucosal and systemic lymphoid organs. Here we provide the first data on the cytokine, antibody and cellular responses to rTsCRT upon in vitro stimulation during taeniasis. PMID:25811778

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

    PubMed Central

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

    2014-01-01

    Background The medicinal leech is considered as a complementary and appropriate model to study immune functions in the central nervous system (CNS). In a context in which an injured leech’s CNS can naturally restore normal synaptic connections, the accumulation of microglia (immune cells of the CNS that are exclusively resident in leeches) has been shown to be essential at the lesion to engage the axonal sprouting. HmC1q (Hm for Hirudo medicinalis) possesses chemotactic properties that are important in the microglial cell recruitment by recognizing at least a C1q binding protein (HmC1qBP alias gC1qR). Material/Methods Recombinant forms of C1q were used in affinity purification and in vitro chemotaxis assays. Anti-calreticulin antibodies were used to neutralize C1q-mediated chemotaxis and locate the production of calreticulin in leech CNS. Results A newly characterized leech calreticulin (HmCalR) has been shown to interact with C1q and participate to the HmC1q-dependent microglia accumulation. HmCalR, which has been detected in only some microglial cells, is consequently a second binding protein for HmC1q, allowing the chemoattraction of resident microglia in the nerve repair process. Conclusions These data give new insight into calreticulin/C1q interaction in an immune function of neuroprotection, suggesting another molecular target to use in investigation of microglia reactivity in a model of CNS injury. PMID:24747831

  14. 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.

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

    PubMed Central

    Allen, S; Bulleid, N J

    1997-01-01

    The roles of the endoplasmic-reticulum lectins calnexin and calreticulin in the folding of tissue-type plasminogen activator (tPA) have been investigated using an in vitro translation system that reconstitutes these processes as they would occur in the intact cell. Using co-immunoprecipitation of newly synthesized tPA with antibodies to calnexin and calreticulin, it was demonstrated that the interaction of tPA with both lectins was dependent upon tPA glycosylation and glucosidase trimming. When tPA was synthesized in the presence of semi-permeabilized cells under conditions preventing complex formation with calnexin and calreticulin, the translation product had a specific plasminogenolytic activity identical with that when synthesized under conditions permitting interactions with both lectins. Furthermore, complexes of tPA bound to calnexin and calreticulin were shown to be enzymically active. These results demonstrate that calnexin and calreticulin can form a stable interaction with correctly folded tPA; however, such interactions are not required for the synthesis of enzymically active tPA. PMID:9359841

  16. 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

  17. Type 1 versus Type 2 calreticulin mutations in essential thrombocythemia: a collaborative study of 1027 patients.

    PubMed

    Tefferi, Ayalew; Wassie, Emnet A; Guglielmelli, Paola; Gangat, Naseema; Belachew, Alem A; Lasho, Terra L; Finke, Christy; Ketterling, Rhett P; Hanson, Curtis A; Pardanani, Animesh; Wolanskyj, Alexandra P; Maffioli, Margherita; Casalone, Rosario; Pacilli, Annalisa; Vannucchi, Alessandro M; Passamonti, Francesco

    2014-08-01

    CALR (calreticulin) trails JAK2 as the second most mutated gene in essential thrombocythemia (ET). Mutant CALR in ET is a result of frameshift mutations, caused by exon 9 deletions or insertions; type-1, 52-bp deletion (p.L367fs*46), and type-2, 5-bp TTGTC insertion (p.K385fs*47) variants constitute more than 80% of these mutations. The current study includes a total of 1027 patients divided into test (n?=?402) and validation (n?=?625) cohorts. Among the 402 ET patients in the test cohort, 227 (57%) harbored JAK2, 11 (3%) Myeloproliferative leukemia virus oncogene (MPL), and 114 (28%) CALR mutations; 12% were wild-type for all three mutations (i.e., triple-negative). Among the 114 patients with CALR mutations, 51 (45%) displayed type-1 and 44 (39%) type-2 variants; compared to mutant JAK2, both variants were associated with higher platelet and lower hemoglobin and leukocyte counts. However, male sex was associated with only type-1 (P?=?0.005) and younger age with type-2 (P?=?0.001) variants. Notably, platelet count was significantly higher in type-2 vs. type-1 CALR-mutated patients (P?=?0.03) and the particular observation was validated in the validation cohort that included 111 CALR-mutated ET patients (P?=?0.002). These findings, coupled with the recent demonstration of preferential expression of mutant and wild-type CALR in megakaryocytes, suggest differential effects of CALR variants on thrombopoiesis. PMID:24753125

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

    PubMed

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

    2014-03-01

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

  19. Molecular analysis of calreticulin expressed in salivary glands of Rhipicephalus (Boophilus) microplus indigenous to Thailand.

    PubMed

    Kaewhom, Paitoon; Stich, Roger W; Needham, Glen R; Jittapalapong, Sathaporn

    2008-12-01

    The tropical cattle tick, Rhipicephalus (Boophilus) microplus, is an important ectoparasite of livestock in Thailand that causes economic losses due to the direct effects of tick feeding and by the pathogens they transmit. Intensive acaricide use has several drawbacks, which spurred efforts to develop anti-tick vaccines. Vaccines targeting concealed antigens localized in the tick midgut result in reduced tick fecundity, but molecules localized in the tick salivary glands, which could play a role in pathogen transmission, remain largely unexplored for R. microplus. Calreticulin (CRT) is a protein found in tick salivary glands and saliva, and CRT might facilitate tick feeding and pathogen transmission through anti-thrombotic and complement-inhibition activities. This then suggests that CRT should be evaluated as a vaccine candidate antigen to control cattle ticks in Thailand. The objective of this work was to clone, sequence, and analyze cDNA encoding CRT from salivary glands of R. microplus indigenous to Thailand. Nucleotide sequence analysis showed an open reading frame of 1233 bp. Comparison of the amino acid sequence showed 65-99% identities to other known CRTs from Oryctolagus cuniculus, Rattus norvegicus, Homo sapiens, Bos taurus, R. sanguineus, and R. microplus. The N- and P-domains of CRT were the most conserved, whereas the C-domain was high acid and more variable. CRT primary sequences were most conserved among mammals. Further investigations are warranted to determine whether immunization with Thai B. microplus CRT can affect tick performances and experimental pathogen transmission. PMID:19120173

  20. Calreticulin functions as a molecular chaperone for the beta-amyloid precursor protein.

    PubMed

    Johnson, R J; Xiao, G; Shanmugaratnam, J; Fine, R E

    2001-01-01

    Processing of the beta-amyloid precursor protein (APP) in the endoplasmic reticulum and the Golgi apparatus may be critical in generating the beta-amyloid molecules linked to the pathogenesis of Alzheimer's disease. Since chaperone molecules such as calreticulin (Crt) have been shown to be important in the maturation of many glycoproteins, we investigated the interaction between Crt and APP. We show that APP binds transiently to Crt in a manner that is pH, divalent cation, and N-linked glycosylation-dependent. Both immature APP (containing only N-linked sugars) and mature APP (containing both N-linked and O-linked sugars) bind to Crt. Both proteins are part of a complex that appears to be large enough to accommodate other proteins as well. However, while most of the immature form is associated with the complexes, very little of the mature form is. The interaction between APP and Crt is likely to be of physiological significance with respect to APP maturation since Crt is involved in quality control of nascent glycoproteins in the secretory pathway. PMID:11378243

  1. 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

  2. Calreticulin associates with non-HLA-A,-B class I proteins in the human choriocarcinoma cell lines JEG-3 and BeWo.

    PubMed Central

    Wainwright, S D; Simpson, K L; Holmes, C H

    1998-01-01

    Human placental trophoblast expresses as unusual repertoire of major histocompatibility complex (MHC) class I products that appears to reflect the unique role of this epithelium in mediating feto-maternal relations during pregnancy. Trophoblast is devoid of human leucocyte antigen (HLA)-A,-B antigens but can express one or more non-HLA-A,-B class I proteins. The human choriocarcinoma cell lines JEG-3, BeWo and JAR are widely used as models to study trophoblast. During attempts to isolate non-HLA-A,-B class I from JEG-3 and BeWo by immunoaffinity chromatography using a monoclonal antibody to beta 2-microglobulin we observed a 55,000 MW protein co-purifying with class I. N-terminal amino acid sequencing and immunoblotting using a specific antiserum identified this product as calreticulin, a molecule recently shown to be involved in the assembly of classical class I in human B-lymphoblastoid cells. In our hands JEG-3 and BeWo were found to express 45,000 MW non-HLA-A,-B class I proteins while the 40,000 MW HLA-G product was identified only in JEG-3. Our data suggest that calreticulin associates with non-HLA-A,-B class I heterodimers and with free 45,000 MW non-HLA-A,-B class I H chains in JEG-3. JAR was found to be devoid of detectable class I H chains but contained beta 2-microglobulin and calreticulin. However, calreticulin-beta 2-microglobulin complexes were not detected in JAR. Calreticulin and class I were apparently co-localized within the endoplasmic reticulum of JEG-3 cells whereas only class I was expressed at the cell surface. These studies demonstrate that calreticulin is associated with non-HLA-A,-B class I products in human choriocarcinoma cells. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 PMID:9640257

  3. Novel evidence of the involvement of calreticulin in major psychiatric disorders.

    PubMed

    Ohadi, M; Mirabzadeh, A; Esmaeilzadeh-Gharehdaghi, E; Rezazadeh, M; Hosseinkhanni, S; Oladnabi, M; Firouzabadi, S Ghasemi; Darvish, H

    2012-06-01

    Calreticulin (CALR) is a multi-functional protein that is strictly conserved across species. Two mRNA transcripts have been recognized for the CALR gene in humans, which use a common promoter sequence. We have recently reported mutations in the CALR promoter that co-occur with psychosis. One of those mutations at -220A increases gene expression in human BE(2)-C and HEK-293 cell lines. This mutation is the first instance of a functional cognition-deficit mutation reversing a human gene promoter to the primitive type. In the current study, we analyzed the effect of the most widely-used mood-stabilizing drug, valproic acid (VPA), on nucleotide -220 in two neuronal cell lines, LAN-5 and N2A. Remarkably, VPA increased gene expression in the cells with the wild-type -220C construct, whereas a dramatic decrease in gene expression was observed in the cell lines with the mutant construct (p<0.000004 and p<0.016, respectively). We also sequenced the 600-bp CALR promoter, and the highly conserved intron 1 sequence in an independent sample of patients afflicted with major psychiatric disorders and controls. A new case of major depressive disorder with psychotic features with the -220A mutation was identified. A novel 1-bp insertion was also detected in intron 1 at IVSI-310, in a case of amphetamine-induced psychosis. As for the psychosis-linked CALR promoter mutations identified to-date, the IVSI mutation was not detected in the control pool. This mutation creates a RREB-1 transcription factor binding site within the first intron. Our present findings identify the site of action of VPA in the CALR promoter, and introduce a novel mutation in a case of substance-induced psychosis in the first intron of CALR. PMID:22507216

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

    PubMed

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

    2014-11-01

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

  5. 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

  6. 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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    PubMed Central

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

    1998-01-01

    SLE is a disease characterized by the presence of multiple autoantibodies and high levels of circulating immune complexes. We studied the presence and functional relevance of autoantibodies directed against a receptor for the collagen-like stalks of the first subcomponent of complement, also known as calreticulin (cC1qR/CaR), in patients with SLE. In a cross-sectional study it was found that higher titres of antibodies against cC1qR/CaR are present in sera of SLE patients compared with normal donors. No association between anti-cC1qR/CaR titres and SLE disease activity was found. Following gel filtration of SLE serum it was found that anti-cC1qR/CaR reactivity is associated with the peak of monomeric IgG. Purified IgG from patients was able to specifically immunoprecipitate cC1qR/CaR. Since we have shown previously that cC1qR/CaR is able to inhibit the haemolytic activity of C1q, we determined a possible pathogenic role for anti-cC1qR/CaR on complement regulation. IgG derived from SLE serum reversed the inhibitory capacity of cC1qR/CaR in a dose-dependent fashion up to 63%, whereas IgG from normal donors had no significant effect. With respect to the capacity of anti-cC1qR/CaR antibodies to activate neutrophils, it was found that incubation of normal neutrophils with F(ab?)2 anti-cC1qR/CaR resulted in a very limited oxidative burst. However, cross-linking of F(ab?)2 anti-cC1qR/CaR on the neutrophils clearly induced neutrophil activation. Pre-incubation of the SLE-derived F(ab?)2 with cC1qR/CaR prevented activation of neutrophils up to 81 ± 5%. These results suggest that the presence of anti-cC1qR/CaR antibodies in patients with SLE may modulate complement and neutrophil activation. PMID:9486404

  9. 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

  10. 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

  11. 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.

  12. 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).

  13. 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

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

    PubMed Central

    2014-01-01

    Background Upper tract urothelial carcinoma (UTUC) is a tumor with sizable metastases and local recurrence. It has a worse prognosis than bladder cancer. This study was designed to investigate the urinary potential tumor markers of UTUC. Methods Between January 2008 and January 2009, urine was sampled from 13 patients with UTUC and 20 healthy adults. The current study identified biomarkers for UTUC using non-fixed volume stepwise weak anion exchange chromatography for fractionation of urine protein prior to two-dimensional gel electrophoresis. Results Fifty five differential proteins have been determined by comparing with the 2-DE maps of the urine of UTUC patients and those of healthy people. Western blotting analysis and immunohistochemistry of tumor tissues and normal tissues from patients with UTUC were carried out to further verify five possible UTUC biomarkers, including zinc-alpha-2-glycoprotein, calreticulin, annexin A2, annexin A3 and haptoglobin. The data of western blot and immunohistochemical analysis are consistent with the 2-DE data. Combined the experimental data in the urine and in tumor tissues collected from patients with UTUC, the crucial over-expressed proteins are calreticulin, annexin A2, and annexin A3. Conclusions Calreticulin, annexin A2, and annexin A3 are very likely a panel of biomarkers with potential value for UTUC diagnosis. PMID:24884814

  15. Catalyzed Ceramic Burner Material

    SciTech Connect

    Barnes, Amy S., Dr.

    2012-06-29

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

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

    PubMed

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

    2013-06-01

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

  17. Frequency and molecular characteristics of calreticulin gene (CALR) mutations in patients with JAK2 -negative myeloproliferative neoplasms.

    PubMed

    Wojtaszewska, Marzena; Iwo?a, Ma?gorzata; Lewandowski, Krzysztof

    2015-01-01

    In 2013, Nangalia et al. and Klampfl et al. found a recurrent and abundant mutation in the calreticulin gene (CALR), mutually exclusive with JAK2 and MPL alterations. At present, the data concerning the new mutation, i.e. its prevalence, allele burden and clinical significance, are scarce. We report the incidence and molecular characteristics of CALR mutations in a group of 184 Polish patients with myeloproliferative neoplasms (MPNs). Clinical data analysis revealed significant differences between JAK2 V617F-mutated and CALR-mutated groups. In essential thrombocythemia patients, hemoglobin levels and leukocyte counts were significantly higher in JAK2-positive than in CALR-positive patients (p = 0.023 and p = 0.017, respectively), but the CALR-positive patients had significantly higher platelet counts (p = 0.022). Patients harboring CALR mutations were also younger at the time of diagnosis (p = 0.039). In primary myelofibrosis patients, the degree of anemia was less severe in those who were CALR exon 9 mutation-positive than in those who were JAK2 V617F-positive (p = 0.048). PMID:25323779

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

    PubMed

    Pop?o?ska, Katarzyna

    2013-02-01

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

  19. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

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

  20. 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. ...

  1. 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

  2. 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

  3. 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.

  4. 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

  5. Roles of calreticulin and calnexin during mucin synthesis in LS180 and HT29/A1 human colonic adenocarcinoma cells.

    PubMed Central

    McCool, D J; Okada, Y; Forstner, J F; Forstner, G G

    1999-01-01

    Molecular chaperones are presumed to associate with large secretory mucin glycoproteins during their synthesis in the endoplasmic reticulum (ER), but have not been identified to date. We decided to look for possible involvement of the chaperones calreticulin (CRT) and calnexin (CLN) during synthesis of two similar gastrointestinal mucins, MUC2 and MUC5AC. Pulse-chase labelling of MUC2 and MUC5AC with [(35)S]methionine/cysteine ([(35)S]Promix) was performed using LS180 and HT29/A1 colonic carcinoma cell lines and was followed by immunoprecipitation with anti-mucin and anti-chaperone antibodies. The precipitated labelled mucin precursors were analysed by SDS/PAGE and autoradiography. Using antibodies specific for each mucin, newly synthesized monomeric precursors of both MUC2 and MUC5AC were detected after a 15 min pulse and then disappeared as oligomers were formed during a 2 h chase period. Only homo-oligomers of MUC2 and MUC5AC were present in the cells. Using anti-CRT, the MUC2 monomeric precursor and oligomer were co-precipitated from both cell lines after a 15 min pulse and the oligomer less strongly after a 0.5 h chase, but there was little co-precipitation after a 2 h chase. At this time, MUC2 immunoprecipitated by anti-MUC2 was completely oligomerized and was endo-beta-N-acetylglucosaminidase-resistant, indicating that the mucin had reached the Golgi region. MUC2 co-precipitated with CRT at zero time and 0.5 h was endo-beta-N-acetylglucosaminidase-sensitive; therefore CRT must have associated with MUC2 in the ER. Treatment with tunicamycin (TUN) diminished the binding of MUC2 to CRT, suggesting a requirement for initial N-glycan addition during this process. Using anti-CLN, only a weak co-precipitation of MUC2, compared with that seen with anti-CRT, was detected in LS180 cells. In contrast with the findings for MUC2, there was no co-precipitation of MUC5AC with CRT or CLN from either cell line at the various time points. In conclusion, CRT and CLN appear to be involved in MUC2 synthesis at the stage of folding and oligomerization in the ER. Since no interaction of the chaperones with MUC5AC was detected at a similar stage of synthesis, these two structurally similar secretory mucins seem to have different chaperone requirements in the ER. PMID:10417322

  6. 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...

  7. 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.

  8. Stau-catalyzed Nuclear Fusion

    E-print Network

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

    2006-10-06

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

  9. Iron Catalyzed Aminohydroxylation of Olefins

    PubMed Central

    Williamson, Kevin S.; Yoon, Tehshik P.

    2010-01-01

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

  10. Iridium-Catalyzed Allylic Substitution

    NASA Astrophysics Data System (ADS)

    Hartwig, John F.; Pouy, Mark J.

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

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

    PubMed

    Wen, Lili; Han, Fan; Shi, Yuxiu

    2015-05-01

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

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

    PubMed

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

    2011-03-30

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

  13. Distribution of a Ca2+ storing site in PtK2 cells during interphase and mitosis. An immunocytochemical study using an antibody against calreticulin.

    PubMed

    Ioshii, S O; Yoshida, T; Imanaka-Yoshida, K; Izutsu, K

    1995-01-01

    To study the distribution of a major Ca(2+)-sequestering site in PtK2 cells, a rat kangaroo kidney epithelial cell line, during interphase and mitosis, we prepared an affinity-purified polyclonal antibody against bovine liver calreticulin (CRT), a major Ca(2+)-binding protein of the endoplasmic reticulum (ER). Immunofluorescence microscopy and immunoperoxidase electron microscopy showed that the anti-CRT antibody labeled a continuous reticular network of the ER and the nuclear envelope in interphase PtK2 cells. The same PtK2 cells double-stained with DiOC6 (3) and the anti-CRT antibody revealed labeling of identical reticular membranes. In contrast to the localization in the ER localization, the mitochondria and the Golgi apparatus were not labeled. These results confirm the exclusive localization of CRT in the ER and that this organelle is a major site for Ca2+ storage in non-muscle cells. In mitotic cells, marked changes of the labeled structure began at prophase-prometaphase and persisted throughout all phases of mitosis. The cytoplasm of the mitotic cells showed diffuse fluorescence, this being more intense around, but not inside, the mitotic spindle. Confocal microscopy and immunoelectron microscopy demonstrated that the CRT-containing membranes changed to segmented tubuloreticular structures, which were concentrated around the mitotic spindle. The ER containing CRT could be responsible for the sequestration of Ca2+ and for the regulation of the concentration of this cation during mitosis, as well as during interphase. PMID:7750522

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

    PubMed Central

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

    2014-01-01

    We have recently reported that soluble calreticulin (CRT) accumulates in the sera of patients with rheumatoid arthritis or systemic lupus erythematosus. Moreover, following self-oligomerization, soluble recombinant CRT (rCRT) polypeptides exhibit potent immunostimulatory activities including macrophage activation in vitro and antibody induction in vivo. This study was designed to further investigate the underlying molecular mechanisms for soluble CRT-induced macrophage activation. Treatment of murine macrophages with oligomerized rCRT (OrCRT) led to (i) TNF-? and IL-6 transcription and protein expression without affecting intracellular mRNA stability; and (ii) I?B? degradation, NF?B phosphorylation and sustained MAPK phosphorylation in cells. Inhibition of IKK and JNK in macrophages substantially abrogated production of TNF-? and IL-6 induced by OrCRT, while ERK suppression only reduced IL-6 expression in parallel experiments. In vitro, fucoidan, a scavenger receptor A (SRA)-specific ligand, significantly reduced the uptake of FITC-labeled OrCRT by macrophages and subsequent MAPK and NF?B activation, thereby suggesting SRA as one of the potential cell surface receptors for soluble CRT. Together, these data indicate that soluble CRT in oligomerized form could play a pathogenic role in autoimmune diseases through induction of pro-inflammatory cytokines (e.g., TNF-? and IL-6) by macrophages via MAPK-NF?B signaling pathway. PMID:24566135

  15. 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

  16. 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

  17. 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, ...

  18. Copper-Catalyzed Trifluoromethylation of Unactivated Olefins

    E-print Network

    Parsons, Andrew T.

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

  19. Calreticulin as a hydrophilic chimeric molecular adjuvant enhances IgG responses to the spike protein of severe acute respiratory syndrome coronavirus.

    PubMed

    Qiu, Xiang; Hong, Chao; Li, Yue; Bao, Wanrong; Gao, Xiao-Ming

    2012-08-01

    Fragment 450-650 of the spike (S) protein (S450-650) of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) contains epitopes capable of being recognized by convalescent sera of SARS patients. Vaccination of mice with recombinant S450-650 (rS450-650) can induce Abs against SARS-CoV, although the titer is relatively low. In the present study, a fusion protein linking a fragment (residues 39-272) of murine calreticulin (CRT) to S450-650 in a prokaryotic expression system was created. Compared with target antigen alone, the recombinant fusion product (rS450-650-CRT) has much improved hydrophilicity and immunogenicity. The S450-650-specific IgG Abs of BALB/c mice subcutaneously immunized with rS450-650-CRT were in substantially higher titer (approximately fivefold more). Furthermore, the fusion protein, but not rS450-650 alone, was able to elicit S450-650-specific IgG responses in T cell deficient nude mice. Given that rCRT/39-272 can drive the maturation of bone-marrow-derived dendritic cells, directly activate macrophages and B cells, and also elicit helper T cell responses in vivo, we propose that fragment 39-272 of CRT is an effective molecular adjuvant capable of enhancing target Ag-specific humoral responses in both a T cell-dependent and independent manner. Fusion protein rS450-650-CRT is a potential candidate vaccine against SARS-CoV infection. PMID:22530918

  20. 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

  1. Anticancer effects of adenovirus-mediated calreticulin and melanoma-associated antigen 3 expression on non-small cell lung cancer cells.

    PubMed

    Liu, Xinli; Sun, Nan; Dong, Yinan; Li, Jijia; Liu, Yang; Ren, Yi; Yang, Chengliang; Zhang, Liang; Zhou, Yang; Tong, Zhuang; Ding, Jianqiao; Zhao, Xiang; Liu, Yu; He, Rong; Xu, Ke; Wu, Yongkai; Huang, Yanfeng; Wang, Hui; Tao, Xiujuan; Liu, Yongyu

    2015-04-01

    Non-small cell lung cancer (NSCLC) is highly prevalent and needs novel therapies. Melanoma-associated antigen 3 (MAGE-A3) is a lung cancer antigen and calreticulin (CALR) can modulate immune responses. Our previous study has shown that up-regulated MAGE-A3 and CALR expression inhibits the proliferation and invasion of glioma cells. In this study, we examined the effect of adenovirus (Ad)-mediated MAGE-A3 and/or CALR expression on the proliferation, invasion, and apoptosis of human NSCLC cells and on the vascular tube formation of human endothelial cells as well as on dendritic cell (DC) activation and induced CD8(+) cytotoxic T lymphocyte (CTL) activity in vitro. We found that low levels of CALR and MAGE-A3 were expressed by A549 cells, but only very low CALR was expressed by DC. Up-regulated CALR and MAGE-A3 expression by infection with Ad-CALR/MAGE-A3 significantly inhibited the proliferation and invasion, but promoted the apoptosis of A549 cells. Up-regulated CALR and MAGE-A3 expression significantly inhibited cyclin D1 expression and the AKT, ERK1/2 and NF-?B expression and phosphorylation in A549 cells. Up-regulated CALR expression inhibited the tube formation in human endothelial cells. Up-regulated CALR and MAGE-A3 expression synergistically enhanced classical DC activation by enhancing IL-12, but reducing IL-10 secretion. Furthermore, CTLs induced by up-regulated CALR and MAGE-A3 expressing DCs synergistically triggered A549 cell apoptosis, which was abrogated by treatment with anti-HLA I, but not anti-HLA II antibodies. Moreover, CTLs induced by CALR and MAGE-A3-expressing DCs had a higher frequency of A549-specific IFN-?-secreting T cells. Our data indicated that up-regulated CALR and MAGE-A3 expression inhibited the carcinogenesis of NSCLC by modulating the AKT, ERK MAPK and NF-?B signaling and enhanced classical DC activation and MAGE-A3-specific CTL cytotoxicity. Therefore, our findings may provide new insights in understanding the role of CALR in modulating antigen-specific T cell immunity and may aid in the design of new therapies for NSCLC. PMID:25704851

  2. 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

  3. 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.

  4. Iron Catalyzed Asymmetric Oxyamination of Olefins

    PubMed Central

    Williamson, Kevin S.; Yoon, Tehshik P.

    2012-01-01

    The regioselective and enantioselective oxyamination of alkenes with N-sulfonyl oxaziridines is catalyzed by a novel iron(II) bis(oxazoline) complex. This process affords oxazolidine products that can be easily manipulated to yield highly enantioenriched free amino alcohols. The regioselectivity of this process is complementary to that obtained from the analogous copper(II)-catalyzed reaction. Thus, both regioisomers of enantioenriched 1,2-aminoalcohols can be obtained using oxaziridine-mediated oxyamination reactions, and the overall sense of regiochemistry can be controlled using the appropriate choice of inexpensive first-row transition metal catalyst. PMID:22793789

  5. Iron catalyzed asymmetric oxyamination of olefins.

    PubMed

    Williamson, Kevin S; Yoon, Tehshik P

    2012-08-01

    The regioselective and enantioselective oxyamination of alkenes with N-sulfonyl oxaziridines is catalyzed by a novel iron(II) bis(oxazoline) complex. This process affords oxazolidine products that can be easily manipulated to yield highly enantioenriched free amino alcohols. The regioselectivity of this process is complementary to that obtained from the analogous copper(II)-catalyzed reaction. Thus, both regioisomers of enantioenriched 1,2-aminoalcohols can be obtained using oxaziridine-mediated oxyamination reactions, and the overall sense of regiochemistry can be controlled using the appropriate choice of inexpensive first-row transition metal catalyst. PMID:22793789

  6. 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.

  7. Transition metal catalyzed borylation of functional ?-systems

    PubMed Central

    SHINOKUBO, Hiroshi

    2014-01-01

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

  8. 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 Wang.003 provides direct support for the proposed mechanism for the rhodium- catalyzed carbene formation from diazo

  9. Palladium catalyzed hydrogenation of bio-oils and organic compounds

    SciTech Connect

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

    2008-09-16

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

  10. Antibody-Catalyzed Degradation of Cocaine

    Microsoft Academic Search

    Donald W. Landry; Kang Zhao; Ginger X.-Q. Yang; Michael Glickman; Taxiarchis M. Georgiadis

    1993-01-01

    Immunization with a phosphonate monoester transition-state analog of cocaine provided monoclonal antibodies capable of catalyzing the hydrolysis of the cocaine benzoyl ester group. An assay for the degradation of radiolabeled cocaine identified active enzymes. Benzoyl esterolysis yields ecgonine methyl ester and benzoic acid, fragments devoid of cocaine's stimulant activity. Passive immunization with such an artificial enzyme could provide a treatment

  11. 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…

  12. Zeolite 5A Catalyzed Etherification of Diphenylmethanol

    ERIC Educational Resources Information Center

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

    2009-01-01

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

  13. Highly Enantioselective Rhodium-Catalyzed Hydrogenation of

    E-print Network

    Zhang, Xumu

    been invented to facili- tate enantioselective catalytic reactions, and unique properties of chiralHighly Enantioselective Rhodium-Catalyzed Hydrogenation of Dehydroamino Acids with New Chiral is the key for the development of highly enantioselective reac- tions. In contrast to many chiral phosphines

  14. Enantioselective iron-catalyzed intramolecular cyclopropanation reactions.

    PubMed

    Shen, Jun-Jie; Zhu, Shou-Fei; Cai, Yan; Xu, Huan; Xie, Xiu-Lan; Zhou, Qi-Lin

    2014-11-24

    An iron-catalyzed asymmetric intramolecular cyclopropanation was realized in high yields and excellent enantioselectivity (up to 97%?ee) by using the iron complexes of chiral spiro-bisoxazoline ligands as catalysts. The superiority of iron catalysts exhibited in this reaction demonstrated the potential abilities of this sustainable metal in asymmetric carbenoid transformation reactions. PMID:25283384

  15. 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

  16. Lysophosphatidylcholine Synthesis by Lipase-catalyzed Ethanolysis.

    PubMed

    Yang, Guolong; Yang, Ruoxi; Hu, Jingbo

    2015-04-01

    Lysophosphatidylcholine (LPC) is amphiphilic substance, and possesses excellent physiological functions. In this study, LPC was prepared through ethanolysis of phosphatidylcholine (PC) in n-hexane or solvent free media catalyzed by Novozym 435 (from Candida antarctica), Lipozyme TLIM (from Thermomcyces lanuginosus) and Lipozyme RMIM (from Rhizomucor miehei). The results showed that three immobilized lipases from Candida Antarctica, Thermomcyces lanuginosus and Rhizomucor miehei could catalyze ethanolysis of PC efficiently. In n-hexane, the LPC conversions of ethanolysis of PC catalyzed by Novozyme 435, Lipozyme TLIM and Lipozyme RMIM could reach to 98.5 ± 1.6%, 94.6 ± 1.4% and 93.7 ± 1.8%, respectively. In solvent free media, the highest LPC conversions of ethanolysis of PC catalyzed by Novozyme 435, Lipozyme TL IM and Lipozyme RM IM were 97.7 ± 1.7%, 93.5 ± 1.2% and 93.8 ± 1.9%, respectively. The catalytic efficiencies of the three lipases were in the order of Novozyme 435 > Lipozyme TLIM > Lipozyme RMIM. Furthermore, their catalytic efficiencies in n-hexane were better than those in solvent free media. PMID:25766935

  17. 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

  18. Heterogeneously-Catalyzed Conversion of Carbohydrates

    NASA Astrophysics Data System (ADS)

    Vigier, Karine De Oliveira; Jérôme, François

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

  19. 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,

  20. Nonmetal catalyzed hydrogenation of carbonyl compounds.

    PubMed

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

    2014-11-12

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

  1. Lipase catalyzed alcoholysis of sunflower oil

    Microsoft Academic Search

    Martin Mittelbach; Karl Franzens

    1990-01-01

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

  2. Antibody-Catalyzed Degradation of Cocaine

    NASA Astrophysics Data System (ADS)

    Landry, Donald W.; Zhao, Kang; Yang, Ginger X.-Q.; Glickman, Michael; Georgiadis, Taxiarchis M.

    1993-03-01

    Immunization with a phosphonate monoester transition-state analog of cocaine provided monoclonal antibodies capable of catalyzing the hydrolysis of the cocaine benzoyl ester group. An assay for the degradation of radiolabeled cocaine identified active enzymes. Benzoyl esterolysis yields ecgonine methyl ester and benzoic acid, fragments devoid of cocaine's stimulant activity. Passive immunization with such an artificial enzyme could provide a treatment for dependence by blunting reinforcement.

  3. 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

  4. Environmental Protection through Energy Efficiency: Catalyzing New Opportunities

    E-print Network

    Silbiger, A.; Smith, J. B.

    ENVIRONMENTAL PROTECTION THROUGH ENERGY EFFICIENCY: CATALYZING NEW OPPORTUNITIES (Abstract Only) Andrew Silbiger, Research Associate, Bruce Company, Washington DC Joel B. Smith, Deputy Division Director, Climate Change Division, U...

  5. Muon-catalyzed [ital pt] fusion

    SciTech Connect

    Baumann, P.; Daniel, H.; Grunewald, S.; Hartmann, F.J.; Lipowsky, R.; Moser, E.; Schott, W.; von Egidy, T. (Physik-Department, Technische Universitaet Muenchen, D-8046 Garching (Germany)); Ackerbauer, P.; Breunlich, W.H.; Fuchs, M.; Jeitler, M.; Kammel, P.; Marton, J.; Naegele, N.; Werner, J.; Zmeskal, J. (Oesterreichische Akademie der Wissenschaften, Institut fuer Mittelenergiephysik,A-1090 Vienna (Austria)); Bossy, H.; Crowe, K.M. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)); Sherman, R.H. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Lou, K.; Petitjean, C. (Paul Scherrer Institut, CH-5232 Villigen (Switzerland)); Markushin, V.E. (Kurchatov Atomic Energy Institute, Moscow 123 182 (Russian Federation))

    1993-06-14

    Gamma rays and, for the first time, conversion muons of [ital pt] fusion have been measured from liquid mixtures of protium, deuterium, and tritium. The rate [lambda][sub 10] for spin flip from the triplet to the singlet state of [ital t][mu](1[ital s]) was found to be [lambda][sub 10]=(1.06[plus minus]0.13)[times]10[sup 3][mu][ital s][sup [minus]1], the rate for muon-catalyzed [ital pt] fusion from the ([ital I]=1) nuclear-spin state to be [lambda][sub [ital p][ital t

  6. 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.

  7. Samarium diiodide-catalyzed diastereoselective pinacol couplings.

    PubMed

    Aspinall, Helen C; Greeves, Nicholas; Valla, Carine

    2005-05-12

    A complex of samarium diiodide (SmI(2)) with tetraglyme catalyzes the intermolecular pinacol coupling of aromatic or aliphatic aldehydes at loadings of 10 mol % in the presence of Me(2)SiCl(2) and Mg. Diastereoselectivity of up to 95/5 (+/-/meso) has been achieved for aliphatic aldehydes and up to 19/81 (+/-/meso) for aromatic aldehydes. De values of up to 99% have been achieved in intramolecular pinacol coupling reactions using the SmI(2)/tetraglyme/Mg/Me(2)SiCl(2) catalytic system. PMID:15876019

  8. Nickel-catalyzed monoarylation of ammonia.

    PubMed

    Borzenko, Andrey; Rotta-Loria, Nicolas L; MacQueen, Preston M; Lavoie, Christopher M; McDonald, Robert; Stradiotto, Mark

    2015-03-16

    Structurally diverse (hetero)aryl chloride, bromide, and tosylate electrophiles were employed in the Ni-catalyzed monoarylation of ammonia, including chemoselective transformations. The employed JosiPhos/[Ni(cod)2 ] catalyst system enables the use of commercially available stock solutions of ammonia, or the use of ammonia gas in these reactions, thereby demonstrating the versatility and potential scalability of the reported protocol. Proof-of-principle experiments established that air-stable [(JosiPhos)NiCl2 ] precatalysts can be employed successfully in such transformations. PMID:25573662

  9. N-Heterocyclic Carbene-Catalyzed Oxidations

    PubMed Central

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

    2009-01-01

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

  10. 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

  11. Titanium-catalyzed C-F activation of fluoroalkenes.

    PubMed

    Kühnel, Moritz F; Lentz, Dieter

    2010-04-01

    Detox: air-stable titanocene difluoride efficiently catalyzes the chemoselective hydrodefluorination of fluoroalkenes at room temperature leading to hydrofluoroalkenes in high yields (see scheme: Cp=cyclopentadienyl). This is a rare example of the catalyzed conversion of fluoroalkenes into less-fluorinated compounds, which have a lower climatic impact, and is a potential method for breaking down toxic perfluoroalkenes. PMID:20229554

  12. 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...

  13. 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

  14. 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.

  15. 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…

  16. Highly Enantioselective Cyclocarbonylation of Allylic Alcohols Catalyzed by Novel

    E-print Network

    Zhang, Xumu

    the first enantioselective variant of this reaction using commercially available chiral bisphosphine ligands enantioselectivity in a number of Rh-BICP and Ru-BICP catalyzed asymmetric hydrogenation reactions.7 These resultsHighly Enantioselective Cyclocarbonylation of Allylic Alcohols Catalyzed by Novel Pd-1

  17. Mammalian Tyrosinase Catalyzes Three Reactions in the Biosynthesis of Melanin

    Microsoft Academic Search

    Ann Korner; John Pawelek

    1982-01-01

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

  18. Enzyme-catalyzed synthesis of aliphatic-aromatic oligoamides.

    PubMed

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

    2013-05-13

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

  19. RNA-Catalyzed RNA Ligation on an External RNA Template

    NASA Technical Reports Server (NTRS)

    McGinness, Kathleen E.; Joyce, Gerald F.

    2002-01-01

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

  20. 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).

  1. 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.

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

    PubMed Central

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

    2006-01-01

    Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne ? complex and is followed by the rate-determining step, which transforms the ? complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five- and six-membered ring endo-cycloisomerizations in the presence of Mo(CO)5 catalyst. The energy barriers calculated for five- and six-membered ring cycloisomerizations are within a range of 25–30 kcal/mol for most cases studied, showing no significant energy difference between the two metals. The stabilization effect of THF and Et3N solvents and the substitution reaction of THF by alkynol substrates in the reaction process with Mo and W complexes are studied as well. The principal difference between Mo- and W-catalyzed cycloisomerization processes appears to be the initial formation of a ? complex, which is more stabilizing for formation of the W-alkyne vs Mo-alkyne complexes. PMID:16601823

  3. 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). ...

  4. Rhodium-catalyzed dehydrogenative borylation of cyclic alkenes

    E-print Network

    Kondoh, Azusa

    A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki–Miyaura ...

  5. ENVIRONMENTAL ASSESSMENT OF THE BASE CATALYZED DECOMPOSITION (BCD) PROCESS

    EPA Science Inventory

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

  6. 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 ...

  7. Electrooxidation of Alcohols Catalyzed by Amino Alcohol Ligated Ruthenium Complexes

    E-print Network

    Zare, Richard N.

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

  8. Palladium-catalyzed direct arylation of phenols with aryl iodides.

    PubMed

    Long, Rongrong; Yan, Xufei; Wu, Zhiqing; Li, Zhengkai; Xiang, Haifeng; Zhou, Xiangge

    2015-03-11

    An efficient protocol of palladium-catalyzed direct para-arylation of unfunctionalized phenols with aryl iodides under mild conditions was reported. A variety of substrates were applied in this reaction with yields up to 87%. PMID:25686911

  9. Palladium-Catalyzed Synthesis of N-Aryl Carbamates

    E-print Network

    Fors, Brett P.

    An efficient synthesis of aryl carbamates was achieved by introducing alcohols into the reaction of palladium-catalyzed cross-coupling of ArX (X = Cl, OTf) with sodium cyanate. The use of aryl triflates as electrophilic ...

  10. The structural basis of RNA-catalyzed RNA polymerization

    E-print Network

    Shechner, David M

    2010-01-01

    The Class I ligase is an artificial ribozyme that catalyzes a reaction chemically identical to a single turnover of RNA-dependent RNA polymerization. Such an activity would have been requisite for the emergence of a ...

  11. 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.

  12. Reaction kinetics of catalyzed competitive heteropolymer cleavage.

    PubMed

    Sadiq, S Kashif; Könnyü, Balázs; Müller, Viktor; Coveney, Peter V

    2011-09-22

    A theoretical formulation for complete heteropolymer degradation is developed in terms of Michaelis-Menten reaction kinetics under the quasi-steady-state approximation. This allows the concentration of the entire intermediate decomposition cascade to be accounted for as well as each species of emerging final product. The formulation is implemented computationally and results in stable reaction kinetics across a range of orders of magnitude for K(M) and k(cat). The model is compared with experiment, specifically in vitro HIV-1 protease-catalyzed retroviral Gag-polyprotein processing. Using an experimentally determined cleavage-polypeptide parameter set, good qualitative agreement is reached with Gag degradation kinetics, given the difference in experimental conditions. A parameter search within 1 order of magnitude of variation of the experimental set results in the determination of an optimal parameter set in complete agreement with experiment which allows the time evolution of each individual as well as intermediate species in Gag to be accurately followed. Future investigations that determine the required enzymatic parameters to populate such a scheme will allow for the model to be refined in order to track the time for viral maturation and infectivity. PMID:21823648

  13. Toluene monooxygenase-catalyzed epoxidation of alkenes.

    PubMed

    McClay, K; Fox, B G; Steffan, R J

    2000-05-01

    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 micromol 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

  14. Biotransformations catalyzed by the genus rhodococcus

    SciTech Connect

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

    1994-01-01

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

  15. Vanadium-Catalyzed C(sp3 )H Fluorination Reactions

    E-print Network

    Chen, Chuo

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

  16. Activated carbon catalyzing the formation of carbon nanotubes

    Microsoft Academic Search

    Jinling Song; Shouai Feng; Jianghong Zhao; Jianfeng Zheng; Zhenping Zhu

    2010-01-01

    Activated carbon (AC), a common carbon material, is employed as catalyst to synthesize carbon nanotubes (CNTs) through chemical vapor deposition (CVD) and detonation-assisted CVD methods. The results show AC can effectively catalyze CNT formation. From the microscopic observations on morphologies and structures of the formed intermediates, it is found that carbon-catalyzed CNT formation follows particle-wire-tube stepwise evolution mechanism, in which

  17. Mechanism of enzyme-catalyzed phospho group transfer

    SciTech Connect

    Hansen, D.E.

    1986-01-01

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

  18. Iron-catalyzed decarboxylative cross coupling reactions and palladium-catalyzed sp2-sp3 coupling of coumarins.

    E-print Network

    Trivedi, Rushi

    2009-12-15

    The thesis details the development of a decarboxylative synthesis of aryl ethers using a relatively new Iron catalyst and a novel decarboxylative coupling of coumarins catalyzed by palladium. Aryl allyl carbonates underwent facile decarboxylative...

  19. 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 ...

  20. 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

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

    2014-04-01

    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

  1. 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

  2. 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.

  3. Graphene oxide catalyzed cis-trans isomerization of azobenzene

    NASA Astrophysics Data System (ADS)

    Shin, Dongha; Kang, Jin Hyoun; Min, Kyung-Ah; Hong, Suklyun; Hee Hong, Byung

    2014-09-01

    We report the fast cis-trans isomerization of an amine-substituted azobenzene catalyzed by graphene oxide (GO), where the amine functionality facilitates the charge transfer from azobenzene to graphene oxide in contrast to non-substituted azobenzene. This catalytic effect was not observed in stilbene analogues, which strongly supports the existence of different isomerization pathways between azobenzene and stilbene. The graphene oxide catalyzed isomerization is expected to be useful as a new photoisomerization based sensing platform complementary to GO-based fluorescence quenching methods.

  4. Molecular Mechanism by which One Enzyme Catalyzes Two Reactions

    NASA Astrophysics Data System (ADS)

    Nishimasu, Hiroshi; Fushinobu, Shinya; Wakagi, Takayoshi

    Unlike ordinary enzymes, fructose-1,6-bisphosphate (FBP) aldolase/phosphatase (FBPA/P) catalyzes two distinct reactions : (1) the aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate to FBP, and (2) the dephosphorylation of FBP to fructose-6-phosphate. We solved the crystal structures of FBPA/P in complex with DHAP (its aldolase form) and FBP (its phosphatase form). The crystal structures revealed that FBPA/P exhibits the dual activities through a dramatic conformational change in the active-site architecture. Our findings expand the conventional concept that one enzyme catalyzes one reaction.

  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. Stereochemistry and Mechanism of Reactions Catalyzed by Tryptophanase from Escherichia coZi*

    E-print Network

    Tsai, Ming-Daw

    base complex of the amino acid and pyridoxal phosphate with elimination of the p substituent (indoleStereochemistry and Mechanism of Reactions Catalyzed by Tryptophanase from Escherichia co reactions catalyzed by tryptophanase from Escherichia coli are shown to proceed stereospecifically

  7. The Resolution of Important Pharmaceutical Building Blocks by Palladium-Catalyzed Aerobic Oxidation of Secondary Alcohols

    E-print Network

    Stoltz, Brian M.

    The Resolution of Important Pharmaceutical Building Blocks by Palladium-Catalyzed Aerobic Oxidation and Mabel Beckman Laboratories of Chemical Synthesis, Division of Chemistry and Chemical Engineering. Abstract: The palladium-catalyzed aerobic oxidative kinetic resolution of key pharmaceutical building

  8. Development and application of transition metal-catalyzed cross-coupling reactions

    E-print Network

    Chae, Junghyun, 1973-

    2004-01-01

    Chapter 1. PALLADIUM-CATALYZED REGIOSELECTIVE HYDRODEBROMINATION OF DIBROMOINDOLES A novel approach to the selective preparation of 4-bromoindoles has been developed via a Pd-catalyzed reaction. A variety of 4,6-dibromoindoles, ...

  9. Flavin-catalyzed insertion of oxygen into rhenium-methyl bonds.

    PubMed

    Pouy, Mark J; Milczek, Erika M; Figg, Travis M; Otten, Brooke M; Prince, Bruce M; Gunnoe, T Brent; Cundari, Thomas R; Groves, John T

    2012-08-01

    Flavins and related molecules catalyze organic Baeyer-Villiger reactions. Combined experimental and DFT studies indicate that these molecules also catalyze the insertion of oxygen into metal-carbon bonds through a Baeyer-Villiger-like transition state. PMID:22827584

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

    E-print Network

    Buschmann, Michael

    Tyrosinase-Catalyzed Synthesis of a Universal Coil-Chitosan Bioconjugate for Protein Immobilization was synthesized using a tyrosinase-catalyzed protocol. Extensive UV/vis and IR characterization demonstrated

  11. Rhodium catalyzed arylation of diazo compounds with aryl boronic acids.

    PubMed

    Ghorai, Jayanta; Anbarasan, Pazhamalai

    2015-04-01

    A general and efficient synthesis of diarylacetate, a diarylmethine derivative, was accomplished through rhodium catalyzed direct arylation of diazo compounds with arylboronic acids. The reaction tolerates various boronic acid derivatives and functional groups. Notably, chemoselective arylation of diazo compounds over other electrophiles were demonstrated. The efficacy of the developed methodology is shown by the expeditious synthesis of the core structure of diclofensine. PMID:25759939

  12. Rhodium catalyzed c2-selective cyanation of indoles and pyrroles.

    PubMed

    Chaitanya, Manthena; Anbarasan, Pazhamalai

    2015-04-01

    An efficient and general rhodium(III) catalyzed C2-selective cyanation of indoles and pyrroles was accomplished employing easily accessible and environmentally friendly cyanating reagent, NCTS. This methodology tolerates various functional groups, uses readily removable directing groups and allows the synthesis of various 2-cyanoindoles and pyrroles in good to excellent yield. PMID:25763805

  13. Mechanistic approaches to palladium-catalyzed alkene difunctionalization reactions

    PubMed Central

    Jensen, Katrina H.; Sigman, Matthew S.

    2009-01-01

    Alkene difunctionalization, the addition of two functional groups across a double bond, exemplifies a class of reactions with significant synthetic potential. This emerging area examines recent developments of palladium-catalyzed difunctionalization reactions, with a focus on mechanistic strategies that allow for functionalization of a common palladium alkyl intermediate. PMID:18972034

  14. Iron(II)-Catalyzed Trifluoromethylation of Potassium Vinyltrifluoroborates

    PubMed Central

    Parsons, Andrew T.; Senecal, Todd D.; Buchwald, Stephen L.

    2012-01-01

    An iron(II)-catalyzed trifluoromethylation of potassium vinyltrifluoroborates has been developed. The reactions proceed under mild conditions and provide E/Z selectivities of > 95:5 for 2-aryl and -heteroarylvinyl substrates. Experimental observations suggest that the reaction does not proceed through a transmetallation of the RBF3K to the iron catalyst. PMID:22328162

  15. Palladium-catalyzed direct arylation of indoles with cyclohexanones.

    PubMed

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

    2014-03-21

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

  16. 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...

  17. 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...

  18. 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 ...

  19. Template-directed oligomerization catalyzed by a polynucleotide analog

    NASA Technical Reports Server (NTRS)

    Visscher, J.; Bakker, C. G.; Van Der Woerd, R.; Schwartz, Alan W.

    1989-01-01

    A pyrophosphate-linked analog of polycytidylic acid has been synthesized and shown to catalyze the oligomerization of the complementary monomer 2'-deoxyguanosine 3',5'-bisphosphoimidazolide. Analogs of polynucleotides are of interest in studies of the origins of life as possible precursors of the first RNA molecules. These results demonstrate that such molecules are capable of serving as templates for further synthesis.

  20. Palladium-Catalyzed ?-Allylation of 2,3-Disubstituted Indoles

    PubMed Central

    Kagawa, Natsuko; Malerich, Jeremiah P.

    2012-01-01

    Given the prevalence of the indole nucleus in biologically active compounds, the direct C3-functionalization of 2,3-disubstituted indoles represents an important problem. Described is a general, high-yielding method for the palladium-catalyzed ?-allylation of carba- and heterocycle fused indoles, including complex natural product substrates. PMID:18491859

  1. Ruthenium-Catalyzed Concurrent Tandem Reactions University of North Carolina

    E-print Network

    Johnson, Jeff S.

    Ruthenium-Catalyzed Concurrent Tandem Reactions Greg Boyce University of North Carolina February 8. Enyne Cascades I. Dienyne Metathesis II. Ring Rearrangement Metathesis III. Metathesis/Non-Metathesis I of Tandem Reactions ­ Sequential tandem reactions involve coupling transformations that operate

  2. Enantioselective Addition of Diethylzinc to Aldehydes Catalyzed by a Titanate

    E-print Network

    Zhang, Xumu

    Enantioselective Addition of Diethylzinc to Aldehydes Catalyzed by a Titanate Complex with a Chiral to aldehydes is one of the most widely studied carbon-carbon bond-forming reac- tions. Many systems reported of diethylzinc to aldehydes (Figure 1).5 Herein we report the scope of this enantioselective reaction

  3. Analysis of enzyme-catalyzed nucleotide modification by aldose reductase

    SciTech Connect

    Grimshaw, C.E.

    1987-05-01

    Homogeneous bovine kidney aldose reductase catalyzes two reactions in addition to the normal aldehyde-dependent oxidation of NADPH. First, adduct formation between the oxidized nucleotide and the oxidized substrate is observed during turnover due to initial formation of a reversible E:NADP/sup +/:R-CHO ternary complex, which subsequently reacts to give the covalent complex (E:NADP/sup +/-R-CHO). The reaction is enzyme-catalyzed with substantial enhancement of both the pseudo-first order rate constant and the overall K/sub eq/ relative to the reaction with free NADP/sup +/ in aqueous buffer. Analysis of the concentration dependence and time-course for reversible dead-end and covalent complex formation are described for several aldehyde and nucleotide substrates. Non-linear time courses for aldehyde reduction and substrate inhibition by the aldehyde substrate in initial velocity studies are completely accounted for by this mechanism, thereby eliminating a simple Dalziel-type explanation for the substrate activation by aldehyde which is also observed. Second, enzyme-catalyzed oxidation of NADPH occurs in the absence of aldehyde substrate with a rate equal to .03% of V/sub max/ for the normal reduction of glyceraldehyde. By 500 MHz /sup 1/H-NMR, the enzyme-catalyzed oxidation of (4-/sup 2/H)NADPH appears to be greater than 95% stereospecific. Spectroscopic evidence for a similar oxidation reaction is observed for the covalent E:NADP/sup +/-R-CHO adduct with glyceraldehyde, but not with glycolaldehyde.

  4. Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols

    E-print Network

    Spino, Claude

    Hydrochloric acid7a and copper(I) chloride6,9b are two frequently utilized acid catalysts for that reaction chloride was incapable of catalyzing their reaction with alcohols, and hydrochloric acid as well as many that would be both mildly Lewis acidic and yet contain ligands capable of acting as a base would procure

  5. 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

  6. 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

  7. Silver-catalyzed protodecarboxylation of heteroaromatic carboxylic acids.

    PubMed

    Lu, Pengfei; Sanchez, Carolina; Cornella, Josep; Larrosa, Igor

    2009-12-17

    A simple and highly efficient protodecarboxylation procedure for a variety of heteroaromatic carboxylic acids catalyzed by Ag(2)CO(3) and AcOH in DMSO is described. This methodology can also perform the selective monoprotodecarboxylation of several aromatic dicarboxylic acids. PMID:19924891

  8. Synthesis of cyclic guanidines via Pd-catalyzed alkene carboamination.

    PubMed

    Zavesky, Blane P; Babij, Nicholas R; Fritz, Jonathan A; Wolfe, John P

    2013-11-01

    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

  9. Metal-Catalyzed Cleavage of tRNA[superscript Phe

    ERIC Educational Resources Information Center

    Kirk, Sarah R.; Silverstein, Todd P.; McFarlane Holman, Karen L.

    2008-01-01

    This laboratory project is one component of a semester-long advanced biochemistry laboratory course that uses several complementary techniques to study tRNA[superscript Phe] conformational changes induced by ligand binding. In this article we describe a set of experiments in which students assay metal-catalyzed hydrolysis of tRNA[superscript Phe]…

  10. Acid-catalyzed dehydrogenation of amine-boranes

    DOEpatents

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

    2010-01-12

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

  11. Surface-Catalyzed Chromium(VI) Reduction: The

    E-print Network

    Deng, Baolin

    Surface-Catalyzed Chromium(VI) Reduction: The TiO2-CrVI-Mandelic Acid System B A O L I N D E N G on chromium solid/solution partitioning and subsurface mi- gration rates. The oxidation of CrIII by molecular

  12. Biocatalysis in Photochemistry Antibody-Catalyzed Enantioselective Norrish

    E-print Network

    Keinan, Ehud

    Biocatalysis in Photochemistry Antibody-Catalyzed Enantioselective Norrish Type II Cyclization** Sigal Saphier, Subhash C. Sinha, and Ehud Keinan* The Norrish type II photochemical reaction involves,4-diradical intermediate, such as A.[1] The latter can undergo three possible reactions: a) reverse hydrogen

  13. 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,…

  14. Neutral Nazarov-Type Cyclization Catalyzed by Pd(0)**

    PubMed Central

    Shimada, Naoyuki; Stewart, Craig; Bow, William F.; Jolit, Anais; Wong, Kahoano; Zhou, Zhe

    2012-01-01

    The first Pd(0)-catalyzed Nazarov-type cyclization of diketoesters proceeds in 70% to 95% yield under strictly neutral conditions. Aryl substitution is not required so the reaction succeeds with aliphatic substrates. The mechanism appears to be novel. A single asymmetric version of this reaction is also reported. PMID:22539448

  15. 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)

  16. Catalyzing Community Efforts for Disaster Reporting, Response and Recovery

    E-print Network

    Shneiderman, Ben

    Catalyzing Community Efforts for Disaster Reporting, Response and Recovery Ben Shneiderman ben Explorer (NLM) ·Doctors ·Surgeons ·Researchers ·Students #12;NASA Environmental Data ·Scientists ·Farmers participation? · Reporting · Response · Recovery #12;How to motivate participation? · Reporting · Response

  17. Gold-catalyzed cyclopropanation reactions using a carbenoid precursor toolbox.

    PubMed

    Qian, Deyun; Zhang, Junliang

    2015-02-01

    Homogeneous gold-catalyzed cyclopropanation has emerged as a powerful method in organic synthesis due to its rich chemistry and fascinating reactivity. This thriving strategy is remarkable for its mild conditions, good selectivity, and high efficiency, which provides complementarity and orthogonality to traditional metal-catalyzed cyclopropanation. This review summarizes recent advances in gold-catalyzed cyclopropanation divided by the type of carbenoid precursors. Besides the commonly used diazo compounds, current approaches enable readily available enynes, propargyl esters, cyclopropenes, cycloheptatrienes, alkynes, and sulfonium ylides as safer surrogates in the realm of gold carbenoid chemistry. Meanwhile, these reactions allow for the rapid building of molecular complexity including synthetically useful and intricate cyclic, heterocyclic, and polycyclic skeletons. The combination of the new reactivity of gold complexes with their capability to catalyze cyclopropanations may lead to myriad opportunities for the design of new reactions. Furthermore, the synthetic utilities of such superior methods have also been illustrated by the total syntheses of selected natural and biologically interesting products and the asymmetric formation of challenging target molecules. PMID:25522173

  18. Diastereoselective Intermolecular Rhodium-Catalyzed [4 + 2 + 2] Carbocyclization Reactions: Computational and Experimental Evidence for

    E-print Network

    Baik, Mu-Hyun

    Diastereoselective Intermolecular Rhodium-Catalyzed [4 + 2 + 2] Carbocyclization Reactions@indiana.edu (M.-H.B.); paevans@indiana.edu (P.A.E.) Intermolecular rhodium-catalyzed [m + n + o] reactions of 1-directed synthesis.1 We recently reported a diastereoselective intermolecular rhodium-catalyzed [4 + 2 + 2

  19. 4-Dimenthylaminopyridine or Acid-Catalyzed Synthesis of Esters: A Comparison

    ERIC Educational Resources Information Center

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

    2006-01-01

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

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

    E-print Network

    He, Chuan

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

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

    E-print Network

    Toste, Dean

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

  2. 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)

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

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  4. 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•.

  5. Iron-catalyzed diboration and carboboration of alkynes.

    PubMed

    Nakagawa, Naohisa; Hatakeyama, Takuji; Nakamura, Masaharu

    2015-03-01

    An iron-catalyzed diboration reaction of alkynes with bis(pinacolato)diboron (B2 pin2 ) and external borating agents (MeOB(OR)2 ) affords diverse symmetrical or unsymmetrical cis-1,2-diborylalkenes. The simple protocol for the diboration reaction can be extended to the iron-catalyzed carboboration of alkynes with primary and, unprecedentedly, secondary alkyl halides, affording various tetrasubstituted monoborylalkenes in a highly stereoselective manner. DFT calculations indicate that a boryliron intermediate adds across the triple bond of an alkyne to afford an alkenyliron intermediate, which can react with the external trapping agents, borates and alkyl halides. In situ trapping experiments support the intermediacy of the alkenyl iron species using radical probe stubstrates. PMID:25631242

  6. 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.

  7. 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

  8. Rearrangement Reactions Catalyzed by Cytochrome P450s

    PubMed Central

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

    2010-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  10. N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones†

    PubMed Central

    Atienza, Roxanne L.; Roth, Howard S.

    2012-01-01

    N-heterocyclic carbenes catalyze the rearrangement of 1,1-bis(arylsulfonyl)ethylene to the corresponding trans-1,2-bis(phenylsulfonyl) under mild conditions. Tandem rearrangement/cycloadditions have been developed to capitalize on this new process and generate highly substituted isoxazolines and additional heterocyclic compounds. Preliminary mechanistic studies support a new conjugate addition/Umpolung process involving the ejection and subsequent unusual re-addition of a sulfinate ion. PMID:22448316

  11. Hydrogen isotope exchange catalyzed by phosphine complexes of palladium

    Microsoft Academic Search

    V. N. Zudin; V. A. Rogov; V. A. Likholobov; V. A. Shmachkov; L. A. Sazonov; Yu. I. Ermakov

    1985-01-01

    1.Bis(triphenylphosphine)bis(trifluoroacetato)palladium in aqueous solutions of trifluoroacetic acid catalyzes the isotope exchange of hydrogen between dihydrogen and the protons of the solvent.2.Hydrogen exchange proceeds through the formation and decomposition of a hydride complex of palladium, the hydrogen atom in which is capable of exchanging with the protons of the solvent.3.The introduction of ethylene into the system lowers the rate of the

  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. Copper-catalyzed trifluoromethylation of trisubstituted allylic and homoallylic alcohols.

    PubMed

    Lei, Jian; Liu, Xiaowu; Zhang, Shaolin; Jiang, Shuang; Huang, Minhao; Wu, Xiaoxing; Zhu, Qiang

    2015-04-27

    An efficient copper-catalyzed trifluoromethylation of trisubstituted allylic and homoallylic alcohols with Togni's reagent has been developed. This strategy, accompanied by a double-bond migration, leads to various branched CF3 -substituted alcohols by using readily available trisubstituted cyclic/acyclic alcohols as substrates. Moreover, for alcohols in which ?-H elimination is prohibited, CF3 -containing oxetanes are isolated as the sole product. PMID:25810003

  14. Lewis acid template-catalyzed asymmetric diels-alder reaction.

    PubMed

    Ishihara, Jun; Nakadachi, Shino; Watanabe, Yuki; Hatakeyama, Susumi

    2015-02-20

    An asymmetric Diels-Alder reaction of 2,4-dienols and methyl acrylate utilizing a chiral Zn(II)/Mg(II) bimetallic template with low catalyst loading was successfully achieved. The bimetallic Lewis acid template derived from (R)-5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol catalyzed the Diels-Alder reaction in the presence of molecular sieves 4 Å to afford various functionalized bicyclic ?-lactones with high enantiomeric purities. PMID:25621816

  15. Frustrated Lewis pair catalyzed hydroamination of terminal alkynes.

    PubMed

    Mahdi, Tayseer; Stephan, Douglas W

    2013-11-18

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

  16. Biaryl Phosphine Ligands in Palladium-Catalyzed Amination

    PubMed Central

    Surry, David S.

    2012-01-01

    Palladium-catalyzed amination of aryl halides has undergone rapid development in the last 12 years. This has been largely driven by implementation of new classes of ligands. Biaryl phosphines have proven to provide especially active catalysts in this context. This review discusses the applications that these catalysts have found in C-N cross-coupling in heterocycle synthesis, pharmaceuticals, materials science and natural product synthesis. PMID:18663711

  17. Ru-Catalyzed Asymmetric Transfer Hydrogenation of ?-Trifluoromethylimines.

    PubMed

    Wu, Meng; Cheng, Tanyu; Ji, Min; Liu, Guohua

    2015-04-01

    Enantioselective transformation of strong electron-withdrawing acyclic ?-trifluoromethylimines to ?-trifluoromethylamines through a ruthenium-catalyzed asymmetric transfer hydrogenation has been developed. The method described here is a facile catalytic process with sodium formate as a hydrogen resource and water-dimethylformamide as a cosolvent. The benefit of this enantioselective transformation affords a series of chiral ?-trifluoromethylamines with high yields and excellent enantioselectivities (93-99% ee) under mild reaction conditions. PMID:25759278

  18. Deglutathionylation of 2-Cys peroxiredoxin is specifically catalyzed by sulfiredoxin.

    PubMed

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

    2009-08-28

    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, Cys(52), Cys(83), and Cys(173) can be glutathionylated in vitro. Deglutathionylation with Cys mutants showed that Cys(83) and Cys(173) were preferentially catalyzed by Srx, with glutathionylated Srx as the reaction intermediate, whereas glutaredoxin I was more favorable for deglutathionylating Cys(52). (ii) Studies using site-directed mutagenesis coupled with binding and deglutathionylation activities revealed that Pro(174) and Pro(179) of Prx I and Tyr(92) 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 H(2)O(2). 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

  19. A Simple Strategy for Glycosyltransferase-Catalyzed Aminosugar Nucleotide Synthesis

    PubMed Central

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

    2014-01-01

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

  20. Pd-catalyzed regioselective allylation of mono- and disubstituted hydrazines.

    PubMed

    Tšupova, Svetlana; Mäeorg, Uno

    2013-07-01

    Palladium-catalyzed allylation of hydrazines using allyl alcohols is reported. This highly efficient protocol furnishes monoallylated hydrazines selectively, in 27-99% yields. Following an optimization of the reaction conditions and of the Pd-ligands, the allylations of both mono- and disubstituted hydrazines were investigated, as well as the effects of C2-substitution on the allylating agent. Of particular interest, a novel method for the selective monoallylation of monosubstituted hydrazines is demonstrated. PMID:23772899

  1. Palladium-catalyzed decarboxylative trifluoroethylation of aryl alkynyl carboxylic acids.

    PubMed

    Hwang, Jinil; Park, Kyungho; Choe, Juseok; Min, Hongkeun; Song, Kwang Ho; Lee, Sunwoo

    2014-04-01

    A trifluoroethylation of alkynes through a palladium-catalyzed decarboxylative coupling reaction was developed. When alkynyl carboxylic acids and ICH2CF3 were allowed to react with [Pd(?(3)-allyl)Cl]2/XantPhos and Cs2CO3 in N,N-dimethylformamide (DMF) at 80 °C for 1 h, the desired products were formed in good yields. This catalytic system showed high functional group tolerance. PMID:24628537

  2. Stereocontrolled O-glycosylation with palladium-catalyzed decarboxylative allylation.

    PubMed

    Xiang, Shaohua; He, Jingxi; Tan, Yu Jia; Liu, Xue-Wei

    2014-12-01

    The Pd-?-allyl intermediate in an electron-rich glycal system with poor reactivity is employed as an efficient glycosyl donor. Starting from glucal derived carbonate, various O-glycosides were formed via a palladium-catalyzed reaction through a tandem decarboxylation, proton abstraction, and nucleophilic addition, in good yields with excellent selectivity. Iterative glycosylation with the same strategy may provide an access to complex oligosaccharides. PMID:25406990

  3. Palladium-Catalyzed Ligand-Directed Oxidative Functionalization of Cyclopropanes

    PubMed Central

    Kubota, Asako; Sanford, Melanie S.

    2015-01-01

    This report describes the Pd-catalyzed functionalization of cyclopropanes containing oxazoline, oxime ether, and pyridine directing groups. Three different oxidants were examined in these studies: IOAc, PhI(OAc)2, and benzoquinone. The reactions yielded products derived from 2° sp3 C–H functionalization and/or C–C activation of the cyclopropane ring. The outcome and the product distributions were highly dependent on the structure of the substrate and the nature of the oxidant.

  4. Copper-catalyzed allylic C-H phosphonation.

    PubMed

    Yang, Bin; Zhang, Hong-Yu; Yang, Shang-Dong

    2015-03-11

    An efficient copper-catalyzed allylic C-H phosphonation reaction has been developed under mild reaction conditions. This method exhibits high regioselectivity and stereoselectivity. Various alkenes with useful functional groups are compatible in this transformation. Preliminary mechanistic studies reveal that the pH value and the loading of Ag-salt were the key factors to change the composition of products. PMID:25679779

  5. 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.

  6. Mechanistic model for the lipase-catalyzed alcoholysis of triacylglycerols

    Microsoft Academic Search

    Fernando Camacho; Alfonso Robles; Pedro A. González; Belén Camacho; Luis Esteban; Emilio Molina

    2006-01-01

    The enzymatic alcoholysis of triolein and an oil highly rich in polyunsaturated fatty acid with ethanol to obtain 2-monoacylglycerols (2-MG) was studied. Two sn-1,3 specific lipases were used to catalyze this reaction: Lipozyme® IM from Mucor miehei and lipase D from Rhizopus oryzae. The experimental results were acceptably fitted to a mechanistic kinetic model that considers the formation of an

  7. Reductive dechlorination catalyzed by bacterial transition-metal coenzymes

    Microsoft Academic Search

    Charles J. Gantzer; Lawrence P. Wackett

    1991-01-01

    The bacterial transition-metal coenzymes vitamin Bââ (Co), coenzyme Fâââ (ni), and hematin (Fe) catalyzed the reductive dechlorination of polychlorinated ethylenes and benzenes, whereas the electron-transfer proteins four-iron ferredoxin, two-iron ferredoxin, and azurin (Cu) did not. For vitamin Bââ and coenzyme Fâââ, reductive dechlorination rates for different classes of perchlorinated compounds had the following order: carbon tetrachloride > tetrachloroethylene > hexachlorobenzene.

  8. Esterification of phenolic acids catalyzed by lipases immobilized in organogels

    Microsoft Academic Search

    M. Zoumpanioti; E. Merianou; T. Karandreas; H. Stamatis; A. Xenakis

    2010-01-01

    Lipases from Rhizomucor miehei and Candida antarctica B were immobilized in hydroxypropylmethyl cellulose organogels based on surfactant-free microemulsions consisting of n-hexane,\\u000a 1-propanol and water. Both lipases kept their catalytic activity, catalyzing the esterification reactions of various phenolic\\u000a acids including cinnamic acid derivatives. High reaction rates and yields (up to 94%) were obtained when lipase from C. antarctica was used. Kinetic

  9. Carica papaya lipase-catalyzed synthesis of terpene esters

    Microsoft Academic Search

    Pengyong You; Erzheng Su; Xuepeng Yang; Duobin Mao; Dongzhi Wei

    2011-01-01

    An efficient approach to synthesize terpene esters using plant lipase-Carica papaya lipase (CPL) as the biocatalyst was developed in this work. The effects of chain length of acyl donor and solvent type on the CPL-catalyzed transesterification reaction were investigated firstly. It was found that CPL showed the highest activity in n-hexane with vinyl octanoate as the best acyl donor. To

  10. Palladium-Catalyzed Synthesis of N-Aryl Carbamates

    PubMed Central

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

    2013-01-01

    An efficient synthesis of aryl carbamates was achieved by introducing alcohols into the reaction of palladium-catalyzed cross-coupling of ArX (X = Cl, OTf) with sodium cyanate. The use of aryl triflates as electrophilic components in this transformation allowed for an expanded substrate scope for direct synthesis of aryl isocyanates. This methodology provides direct access to major carbamate protecting groups, S-thiocarbamates, and diisocyanate precursors to polyurethane materials. PMID:23441814

  11. Highly enantioselective nickel-catalyzed intramolecular reductive cyclization of alkynones.

    PubMed

    Fu, Wenzhen; Nie, Ming; Wang, Aizhen; Cao, Ziping; Tang, Wenjun

    2015-02-16

    The first asymmetric nickel-catalyzed intramolecular reductive cyclization of alkynones is reported. A P-chiral monophosphine and triethylsilane were used as the ligand and the reducing reagent, respectively, to form a series of tertiary allylic alcohols bearing furan/pyran rings in excellent yields and enantioselectivities. This reaction has a broad substrate scope and enabled the efficient synthesis of dehydroxycubebin and chiral dibenzocyclooctadiene skeletons. PMID:25597850

  12. Unexpected copper-catalyzed cascade synthesis of quinazoline derivatives.

    PubMed

    Chen, Zhongyan; Chen, Jiuxi; Liu, Miaochang; Ding, Jinchang; Gao, Wenxia; Huang, Xiaobo; Wu, Huayue

    2013-11-15

    The first example of a copper-catalyzed cascade reaction of (2-aminophenyl)methanols with aldehydes using the combination of cerium nitrate hexahydrate and ammonium chloride has been developed, leading to a wide range of 2-substituted quinazolines in moderate to excellent yields. The efficiency of this transformation was demonstrated by compatibility with a wide range of functional groups. Thus, the method represents a convenient and practical strategy for synthesis of 2-substituted quinazoline derivatives. PMID:24134489

  13. Stereochemical course of hydrolysis catalyzed by arabinofuranosyl hydrolases

    Microsoft Academic Search

    Stuart M. Pitson; Alphons G. J. Voragen; Gerrit Beldman

    1996-01-01

    The stereochemical course of hydrolysis catalyzed by various enzymes acting on arabinofuranosyl linkages has been determined. 1H-NMR analysis of the action of endo-(1 ? 5)-?-l-arabinanases from Aspergillus niger and Aspergillus aculeatus showed that both hydrolyze linear arabinan with inversion of configuration, and may therefore act via a single displacement mechanism. This is consistent with the A. niger enzyme's classification in

  14. Base-Catalyzed Oxidation of Carboxymethylcellulose Polymer by Permanganate

    Microsoft Academic Search

    Ali M. Shaker

    2001-01-01

    The kinetics and mechanism of the disproportionation of MnO4? via [CMC–MnVIO42?] intermediate complex formation during the oxidation of carboxymethyl-cellulose (CMC) polysaccharide have been investigated spectrophotometrically at pH?12 and various temperatures (15–35°C). The rate law was suggested as rate=kobs[MnO4?]. Kinetic and spectrophotometric measurements revealed the base-catalyzed formation of manganate(VI) transient species. A mechanism was postulated consistent with the experimental data.

  15. Pd-catalyzed nucleophilic fluorination of aryl bromides.

    PubMed

    Lee, Hong Geun; Milner, Phillip J; Buchwald, Stephen L

    2014-03-12

    On the basis of mechanism-driven reaction design, a Pd-catalyzed nucleophilic fluorination of aryl bromides and iodides has been developed. The method exhibits a broad substrate scope, especially with respect to nitrogen-containing heteroaryl bromides, and proceeds with minimal formation of the corresponding reduction products. A facilitated ligand modification process was shown to be critical to the success of the reaction. PMID:24559304

  16. Cobalt porphyrin-catalyzed alkane oxidations using dioxygen as oxidant

    Microsoft Academic Search

    Hui Tang; Chengyu Shen; Minren Lin; Ayusman Sen

    2000-01-01

    In a mixture of trifluoroacetic acid and water, cobalt(II) porphyrin complexes catalyze the oxidation of alkanes by dioxygen. Carbon monoxide is required as a coreductant for the oxidations to proceed. While the turnover rates are slow, the system displays unusual selectivity in that primary C?H bonds are more reactive than the weaker secondary C?H bonds or C?H bonds ? to

  17. 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

  18. Vanadium haloperoxidase-catalyzed bromination and cyclization of terpenes.

    PubMed

    Carter-Franklin, Jayme N; Parrish, Jon D; Tschirret-Guth, Richard A; Little, R Daniel; Butler, Alison

    2003-04-01

    Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products, including cyclic terpenes. The biogenesis of certain cyclic halogenated marine natural products is thought to involve marine haloperoxidase enzymes. Evidence is presented that vanadium bromoperoxidase (V-BrPO) isolated and cloned from marine red algae that produce halogenated compounds (e.g., Plocamium cartilagineum, Laurencia pacifica, Corallina officinalis) can catalyze the bromination and cyclization of terpenes and terpene analogues. The V-BrPO-catalyzed reaction with the monoterpene nerol in the presence of bromide ion and hydrogen peroxide produces a monobromo eight-membered cyclic ether similar to laurencin, a brominated C15 acetogenin, from Laurencia glandulifera, along with noncyclic bromohydrin, epoxide, and dibromoproducts; however, reaction of aqueous bromine with nerol produced only noncyclic bromohydrin, epoxide, and dibromoproducts. The V-BrPO-catalyzed reaction with geraniol in the presence of bromide ion and hydrogen peroxide produces two singly brominated six-membered cyclic products, analogous to the ring structures of alpha and beta snyderols, brominated sesquiterpenes from Laurencia, spp., along with noncyclic bromohydrin, epoxide, and dibromoproducts; again, reaction of geraniol with aqueous bromine produces only noncyclic bromohydrin, epoxide, and dibromoproducts. Thus, V-BrPO can direct the electrophilic bromination and cyclization of terpenes. PMID:12656585

  19. 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.

  20. Calreticulin mutations in Chinese with primary myelofibrosis.

    PubMed

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

    2014-11-01

    We tested 357 Chinese with primary myelofibrosis for mutations in CALR, JAK2 and MPL. CALR mutations were detected in 76 subjects (21%). There were 24 (32%) type-1 (L367fs*46) and 49 (64%) type-2 (K385fs*47) mutations. Seventy-two of 168 subjects (43%) without a JAK2 or MPL mutation had a CALR mutation. Subjects with a type-2 CALR mutation had lower hemoglobin concentrations (P=0.001), lower WBC counts (P<0.001), a higher percentage of blood blasts (P=0.009), and higher conventional (P<0.001) and Chinese-adjusted Dynamic International Prognostic Scoring System (P<0.001) scores compared with subjects with JAK2 mutations. Subjects with a type-2 CALR mutation were also likely to have abnormal platelet levels (<100 × 10(9)/L, P=0.01 or >450 × 10(9)/L, P=0.042) and no splenomegaly (P=0.004). Type-2 CALR mutation or no detectable mutation was an independent high-risk factor for survival in multivariate analyses. These data suggest the ratio between type-1 and type-2 mutations is reversed in Chinese with primary myelofibrosis compared with populations of subjects with primary myelofibrosis of predominately European descent. The unfavorable prognostic impact of CALR mutations in Chinese with primary myelofibrosis is only seen in those with type-2 mutations. These data underscore the need to evaluate the prognostic impact of genetic mutations in different populations. PMID:24997152

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

    PubMed Central

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

    2011-01-01

    We report a concise, enantioselective total synthesis of (?)-taiwaniaquinone H and the first enantioselective total synthesis of (?)-taiwaniaquinol B by a route that includes enantioselective, palladium-catalyzed ?-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C–H borylation. This asymmetric ?-arylation creates the benzylic, quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic, quaternary, stereogenic centers, even those lacking a carbonyl group in the ?-position, by asymmetric ?-arylation. PMID:21268578

  2. Mechanism investigation of catalyzed ozonation of 2-methylisoborneol in drinking water over aluminum (hydroxyl) oxides: Role of surface hydroxyl group

    Microsoft Academic Search

    Fei Qi; Bingbing Xu; Zhonglin Chen; Liqiu Zhang; Panyue Zhang; Dezhi Sun

    2010-01-01

    In this investigation, the mechanism of catalyzed ozonation of MIB by aluminum oxides (?-AlOOH and ?-Al2O3) was studied. It was concluded that the roles of surface hydroxyl groups in adsorption and catalyzed ozonation determined catalyzed ozonation mechanism. The removal efficiency of MIB in catalyzed ozonation by ?-Al2O3 or ?-AlOOH was 98.4% and 27.5%, respectively. Effect of water pH on catalyzed

  3. Mechanism of the reaction catalyzed by mandelate racemase. 3. Asymmetry in reactions catalyzed by the H297N mutant

    SciTech Connect

    Landro, J.A.; Kallarakal, A.T.; Ransom, S.C.; Gerlt, J.A.; Kozarich, J.W. (Univ. of Maryland, College Park (United States)); Neidhart, D.J. (Abbott Labs., Abbott Park, IL (United States)); Kenyon, G.L. (Univ. of California, San Francisco (United States))

    1991-09-24

    Two preceding papers suggest that the active site of mandelate racemase (MR) contains two distinct general acid/base catalysts: Lys 166, which abstracts the {alpha}-proton from (s)-mandelate, and His 297, which abstracts the {alpha}-proton from (R)-mandelate. In this paper the authors report on the properties of the mutant of MR in which His 297 has been converted to asparagine by site-directed mutagenesis (H297N). The structure of H297N, solved by molecular replacement at 2.2-{angstrom} resolution, reveals that no conformational alterations accompany the substitution. As expected, h297N has no detectable MR activity. However, H297N catalyzes the stereospecific elimination of bromide ion from racemic {rho}-(bromomethyl) mandelate to give {rho}-(methyl)-benzoylformate in 45% yield at a rate equal to that measured for wild-type enzyme. The pD dependence of the rate of the exchange reaction catalyzed by H297N reveals a pK{sub a} of 6.4 in D{sub 2}O which is assigned to Lys 166. These observations provide persuasive evidence that the reaction catalyzed by MR does, in fact, proceed via a two-base mechanism in which Lys 166 abstracts the {alpha}-proton from (S)-mandelate and His 297 abstracts the {alpha}-proton from (R)-mandelate. These studies demonstrate the power of site-directed mutagenesis in providing otherwise inaccessible detail about the mechanism of an enzyme-catalyzed reaction.

  4. Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.

    PubMed

    Alcaide, Benito; Almendros, Pedro

    2014-03-18

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

  5. Iodine-catalyzed oxidative coupling reactions utilizing c?h and x?h as nucleophiles.

    PubMed

    Liu, Dong; Lei, Aiwen

    2015-04-01

    In recent decades, iodine-catalyzed oxidative coupling reactions utilizing C?H and X?H as nucleophiles have received considerable attention because they represent more efficient, greener, more atom-economical, and milder bond-formation strategies over transition-metal-catalyzed oxidative coupling reactions. This Focus Review gives a brief summary of recent development on iodine-catalyzed oxidative coupling reactions utilizing C?H and X?H as nucleophiles. PMID:25683644

  6. Quantum chemical modeling of the epoxidation with hydrogen peroxide catalyzed by Mn(III): Mechanistic insight

    NASA Astrophysics Data System (ADS)

    Zhou, Shaodong; Chen, Xinzhi; Qian, Chao

    2010-03-01

    Styrene epoxidation with hydrogen peroxide catalyzed by Mn(III) complex was studied using DFT calculation method. The previous mechanisms of metal complex-catalyzed epoxidation were found unsuitable for the Mn(III) complex used in this work. Reasonable mechanisms were proposed and investigated. Lowering of barrier was found in catalyzed reaction. The side reaction, oxidation of styrene, was also investigated. The Gibbs energy changes of epoxidation and oxidation were calculated to give a general prediction of product distribution.

  7. A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes

    SciTech Connect

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

    2012-01-01

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

  8. A Link between Protein Structure and Enzyme Catalyzed Hydrogen Tunneling

    NASA Astrophysics Data System (ADS)

    Bahnson, Brian J.; Colby, Thomas D.; Chin, Jodie K.; Goldstein, Barry M.; Klinman, Judith P.

    1997-11-01

    We present evidence that the size of an active site side chain may modulate the degree of hydrogen tunneling in an enzyme-catalyzed reaction. Primary and secondary kH/kT and kD/kT kinetic isotope effects have been measured for the oxidation of benzyl alcohol catalyzed by horse liver alcohol dehydrogenase at 25 degrees C. As reported in earlier studies, the relationship between secondary kH/kT and kD/kT isotope effects provides a sensitive probe for deviations from classical behavior. In the present work, catalytic efficiency and the extent of hydrogen tunneling have been correlated for the alcohol dehydrogenase-catalyzed hydride transfer among a group of site-directed mutants at position 203. Val-203 interacts with the opposite face of the cofactor NAD+ from the alcohol substrate. The reduction in size of this residue is correlated with diminished tunneling and a two orders of magnitude decrease in catalytic efficiency. Comparison of the x-ray crystal structures of a ternary complex of a high-tunneling (Phe-93 --> Trp) and a low-tunneling (Val-203 --> Ala) mutant provides a structural basis for the observed effects, demonstrating an increase in the hydrogen transfer distance for the low-tunneling mutant. The Val-203 --> Ala ternary complex crystal structure also shows a hyperclosed interdomain geometry relative to the wild-type and the Phe-93 --> Trp mutant ternary complex structures. This demonstrates a flexibility in interdomain movement that could potentially narrow the distance between the donor and acceptor carbons in the native enzyme and may enhance the role of tunneling in the hydride transfer reaction.

  9. Enantioselective Rhodium-Catalyzed Allylation of Cyclic Imines with Potassium Allyltrifluoroborates 

    E-print Network

    Hepburn, Hamish B.; Chotsaeng, Nawasit; Luo, Yunfei; Lam, Hon Wai

    2013-01-01

    This Article presents further examples of the enantioselective rhodium-catalyzed addition of potassium allyltrifluoroborates to cyclic imines. A wide range of substituted allyltrifluoroborates are compatible with this ...

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

    DOEpatents

    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.

  11. Mechanism of rhodium-catalyzed cyclopropanation/cyclization of allenynes.

    PubMed

    Huang, Genping

    2015-04-17

    The rhodium-catalyzed cyclopropanation/cyclization of allenynes was investigated by means of DFT calculations. The results show that the cyclopropanation via the proposed stepwise C(sp(3))-H activation (?-bond metathesis/C-H reductive elimination) was kinetically unfavorable. Instead, a concerted C(sp(3))-H activation pathway, namely the metal-assisted ?-bond metathesis, in which the hydrogen was directly transferred to the rhodacyclopentane assisted by the Rh center followed by a C-C reductive elimination, was found to explain the experimental results. PMID:25849445

  12. Organoborane catalyzed regioselective 1,4-hydroboration of pyridines.

    PubMed

    Fan, Xiaoting; Zheng, Junhao; Li, Zhen Hua; Wang, Huadong

    2015-04-22

    A bulky organoborane Ar(F)2BMe (Ar(F) = 2,4,6-tris(trifluoromethyl)phenyl, 1) has been synthesized. In C6D6 solution this organoborane and pyridine form a frustrated Lewis pair. Under mild conditions, 1 can efficiently catalyze 1,4-hydroboration of a series of pyridines. This reaction is highly chemo- and regioselective. The reaction intermediate, a boronium complex [Py2Bpin][Ar(F)2B(H)Me] (3), was characterized in solution by NMR spectroscopy, which was also confirmed by DFT calculation. PMID:25846625

  13. The Palladium-Catalyzed Trifluoromethylation of Vinyl Sulfonates

    PubMed Central

    Cho, Eun Jin; Buchwald, Stephen L.

    2011-01-01

    A method for the palladium-catalyzed trifluoromethylation of cyclohexenyl sulfonates has been developed. Various cyclohexenyl triflates and nonaflates underwent trifluoromethylation under mild reaction conditions using a catalyst system composed of Pd(dba)2 or [(allyl)PdCl]2 and the monodentate biaryl phosphine ligand tBuXPhos. The trifluoromethyl anion (CF3?) or its equivalent for the process was generated in situ from TMSCF3 in combination with KF or TESCF3 in combintion with RbF. PMID:22111687

  14. Stau-catalyzed d-t Nuclear Fusion

    E-print Network

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

    2012-02-13

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

  15. Copper-catalyzed selective arylations of benzoxazoles with aryl iodides.

    PubMed

    Kim, Donghae; Yoo, Kwangho; Kim, Se Eun; Cho, Hee Jin; Lee, Junseong; Kim, Youngjo; Kim, Min

    2015-04-01

    A copper-catalyzed direct ring-opening double N-arylation of benzoxazoles with aryl iodides has been developed. The present system exhibits high selectivity despite competition from C-arylation. The selectivity between ring-opening N-arylation and C-arylation was controlled by the choice of reaction vessel. The nitrile bound bis(triphenylphosphine)copper cyanide was identified as the active catalytic species for both reactions, and when combined with a nitrile-containing solvent, enhanced the reaction efficiency. PMID:25768792

  16. Ruthenium catalyzed hydroboration of terminal alkynes to Z-vinylboronates.

    PubMed

    Gunanathan, Chidambaram; Hölscher, Markus; Pan, Fangfang; Leitner, Walter

    2012-09-01

    The nonclassical ruthenium hydride pincer complex [Ru(PNP)(H)(2)(H(2))] 1 (PNP = 1,3-bis(di-tert-butyl-phosphinomethyl)pyridine) catalyzes the anti-Markovnikov addition of pinacolborane to terminal alkynes yielding Z-vinylboronates at mild conditions. The complex [Ru(PNP)(H)(2)(HBpin)] 2 (HBpin = pinacolborane), which was identified at the end of the reaction and prepared independently, is proposed as the direct precursor to the catalytic cycle involving rearrangement of coordinated alkyne to Z-vinylidene as a key step for the apparent trans-hydroboration. PMID:22913738

  17. Muon catalyzed fusion in deuterium at 3 K

    SciTech Connect

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

    1995-12-01

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

  18. Base-Catalyzed Depolymerization of Lignin: Separation of Monomers

    SciTech Connect

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

    2007-12-01

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

  19. Copper-catalyzed N-arylation of imidazoles and benzimidazoles.

    PubMed

    Altman, Ryan A; Koval, Erica D; Buchwald, Stephen L

    2007-08-01

    4,7-Dimethoxy-1,10-phenanthroline (L1c) was found to be an efficient ligand for the copper-catalyzed N-arylation of imidazoles and benzimidazoles with both aryl iodides and bromides under mild conditions. Further optimization of the system has revealed that the addition of poly(ethylene glycol) accelerates this reaction. A variety of hindered and functionalized imidazoles, benzimidazoles, and aryl halides were transformed in good to excellent yields. Heteroaryl halides were also coupled in moderate to good yields. We also present the results obtained from a series of coupling reactions, which directly compare the use of L1c with other recently reported ligands. PMID:17625886

  20. Nickel(0)-catalyzed asymmetric hydrocyanation of 1,3-dienes.

    PubMed

    Saha, Biswajit; Rajanbabu, T V

    2006-09-28

    1,2-Bis-diarylphosphinites are excellent ligands for the Ni(0)-catalyzed hydrocyanation of certain types of 1,3-dienes. 1-Phenyl-1,3-butadiene, 1-vinyl-3,4-dihydronaphthalene, and 1-vinylindene undergo highly regioselective hydrocyanation under ambient conditions to give exclusively the 1,2-adducts in good to excellent yields. Using bis-1,2-diarylphosphinites derived from d-glucose, the highest enantioselectivities to-date for asymmetric hydrocyanation of 1,3-dienes (70-83% ee's) have been obtained. PMID:16986974

  1. Thermodynamics of industrially-important, enzyme-catalyzed reactions

    Microsoft Academic Search

    Yadu B. Tewari

    1990-01-01

    The thermodynamics of 10 industrially-important, enzyme-catalyzed reactions are examined. The reactions discussed are: the\\u000a conversions of penicillin G to 6-amino-penicillinic acid using the enzyme penicillin acylase; starch to glucose using amylases;\\u000a glucose to fructose using glucose (xylose) isomerase; cellulose to glucose using cellulase; fumaric acid and ammonia to l-aspartic\\u000a acid using l-aspartase; transcinnamic acid and ammonia to l-phenylalanine using l-phenylalanine

  2. Acid-catalyzed oxidative radical addition of ketones to olefins.

    PubMed

    Schweitzer-Chaput, Bertrand; Demaerel, Joachim; Engler, Hauke; Klussmann, Martin

    2014-08-11

    Based on a mechanistic study, we have discovered a Brønsted acid catalyzed formation of ketone radicals. This is believed to proceed via thermally labile alkenyl peroxides formed in situ from ketones and hydroperoxides. The discovery could be utilized to develop a multicomponent radical addition of unactivated ketones and tert-butyl hydroperoxide to olefins. The resulting ?-peroxyketones are synthetically useful intermediates that can be further transformed into 1,4-diketones, homoaldol products, and alkyl ketones. A one-pot reaction yielding a pharmaceutically active pyrrole is also described. PMID:24777703

  3. 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

  4. Oxidations catalyzed by osmium compounds. Part 1: Efficient alkane oxidation with peroxides catalyzed by an olefin carbonyl osmium(0) complex

    Microsoft Academic Search

    Georgiy B. Shul’pin; Aleksandr R. Kudinov; Lidia S. Shul’pina; Elena A. Petrovskaya

    2006-01-01

    A carbonyl osmium(0) complex with ?-coordinated olefin, (2,3-?-1,4-diphenylbut-2-en-1,4-dione)undecacarbonyl triangulotriosmium (1), efficiently catalyzes oxygenation of alkanes (cyclohexane, cyclooctane, n-heptane, isooctane, etc.) with hydrogen peroxide, as well as with tert-butyl hydroperoxide and meta-chloroperoxybenzoic acid in acetonitrile solution. Alkanes are oxidized to corresponding alcohols, ketones (aldehydes) and alkyl hydroperoxides. Thus, heating cyclooctane with the 1–H2O2 combination at 70°C gave products with turnover number

  5. Self-regulated pulsed nucleation in catalyzed nanowire growth

    NASA Astrophysics Data System (ADS)

    Dubrovskii, V. G.

    2013-05-01

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

  6. 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

  7. Ionic Liquid Catalyzed Electrolyte for Electrochemical Polyaniline Supercapacitors

    NASA Astrophysics Data System (ADS)

    Inamdar, A. I.; Im, Hyunsik; Jung, Woong; Kim, Hyungsang; Kim, Byungchul; Yu, Kook-Hyun; Kim, Jin-Sang; Hwang, Sung-Min

    2013-05-01

    The effect of different wt.% of ionic liquid "1,6-bis (trimethylammonium-1-yl) hexane tetrafluoroborate" in 0.5 M LiClO4+PC electrolyte on the supercapacitor properties of polyaniline (PANI) thin film are investigated. The PANI film is synthesized using electropolymerization of aniline in the presence of sulfuric acid. The electrochemical properties of the PANI thin film are studied by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) measurements. The optimum amount of the ionic liquid is found to be 2 wt.% which provides better ionic conductivity of the electrolyte. The highest specific capacitance of 259 F/g is obtained using the 2 wt.% electrolyte. This capacitance remains at up to 208 F/g (80% capacity retention) after 1000 charge-discharge cycles at a current density of 0.5 mA/g. The PANI film in the 2 wt.% ionic liquid catalyzed 0.5 M LiClO4+PC electrolyte shows small electrochemical resistance, better rate performance and higher cyclability. The increased ionic conductivity of the 2 wt.% ionic liquid catalyzed electrolyte causes a reduction in resistance at the electrode/electrolyte interface, which can be useful in electrochemically-preferred power devices for better applicability.

  8. Lipase-catalyzed polyester synthesis – A green polymer chemistry

    PubMed Central

    Kobayashi, Shiro

    2010-01-01

    This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’. PMID:20431260

  9. 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.

  10. Porous silicon formation during Au-catalyzed etching

    SciTech Connect

    Algasinger, Michael; Bernt, Maximilian; Koynov, Svetoslav; Stutzmann, Martin [Walter Schottky Institut, Technische Universität München, 85748 Garching (Germany)

    2014-04-28

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

  11. Muon catalyzed fusion: old and new aspects of energy production

    NASA Astrophysics Data System (ADS)

    Daniel, H.

    1993-03-01

    Muon catalyzed fusion of deuterium and tritium (?CF) yields the same energy gain per reaction as fusion with magnetic or inertial confinement (17.6 MeV). The crucial points of ?Cf are, however, very different, namely (a) the energy cost W (?) for production of one ?- and (b) the number n of reactions a single muon can catalyze on the average. (b) is ultimately limited by the effective sticking probability ? f : n?1/ ? f. With “standard” methods one has W (?)?5 GeV, ? f=0.5%. Hence a “standard” ?CF reactor can never reach a net energy gain. To solve this problem, ways discussed since about a decade are to increase the efficiency by both (i) energy multiplication using a fissionable blanket and (ii) breeding. A new way to increase the safety of fission devices mostly due to Yu. Petrov is outlined. On the other hand there is a hope to lower W (?) slightly and ? f drastically, the latter by artificial reactivation. New theoretical results for beam cooling in an omegatron type driven integrated ?CF reactor, important for W (?) and, in particular, ? f, is presented.

  12. 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.

  13. Rh(I)-catalyzed benzo/[7+1] cycloaddition of cyclopropyl-benzocyclobutenes and CO by merging thermal and metal-catalyzed C-C bond cleavages.

    PubMed

    Fu, Xu-Fei; Xiang, Yu; Yu, Zhi-Xiang

    2015-03-01

    A Rh-catalyzed benzo/[7+1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to benzocyclooctenones has been developed. In this reaction, CP-BCB acts as a benzo/7-C synthon and the reaction involves two C-C bond cleavages: a thermal electrocyclic ring-opening of the four-membered ring in CP-BCB and a Rh-catalyzed C-C cleavage of the cyclopropane ring. PMID:25612241

  14. Rhodium-Catalyzed Asymmetric Arylation of Allyl Sulfones under the Conditions of Isomerization into Alkenyl Sulfones.

    PubMed

    Lim, Kelvin Meng-Hui; Hayashi, Tamio

    2015-03-11

    The reaction of 3-sulfolene with arylboronic acids in the presence of a chiral diene-rhodium catalyst under highly basic conditions (10 equiv of KOH) gave high yields of 3-arylsulfolanes with high enantioselectivity, where 3-sulfolene is in equilibration with 2-sulfolene by base-catalyzed isomerization and the more reactive 2-sulfolene undergoes the rhodium-catalyzed asymmetric arylation. PMID:25706689

  15. Novel Rhodium-Catalyzed Cycloisomerization of 1,6-Enynes with an Intramolecular Halogen Shift

    E-print Network

    Zhang, Xumu

    Novel Rhodium-Catalyzed Cycloisomerization of 1,6-Enynes with an Intramolecular Halogen Shift involving a -allyl rhodium complex has not been reported. Herein, we report a new Rh-catalyzed 1,6-enyne cyclization process with a -allyl rhodium as the key intermediate. It is noteworthy that a halogen shift

  16. 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

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

    E-print Network

    Toste, Dean

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

  18. Nickel-catalyzed amination of aryl chlorides with ammonia or ammonium salts.

    PubMed

    Green, Rebecca A; Hartwig, John F

    2015-03-16

    The nickel-catalyzed amination of aryl chlorides to form primary arylamines occurs with ammonia or ammonium sulfate and a well-defined single-component nickel(0) precatalyst containing a Josiphos ligand and an ?(2) -bound benzonitrile ligand. This system also catalyzes the coupling of aryl chlorides with gaseous amines in the form of their hydrochloride salts. PMID:25711163

  19. Palladium catalyzed selective mono-arylation of o-carboranes via B-H activation.

    PubMed

    Cao, Ke; Huang, Yawen; Yang, Junxiao; Wu, Ji

    2015-04-01

    Palladium catalyzed selective mono-arylation of o-carboranes with aryl iodides has been developed, and a series of B(8)/B(9)-Ar-o-carboranes anchored with active groups have been synthesized with moderate to good yield as well as good selectivity. The mechanism involving Pd(II) catalyzed electrophilic B-H activation was also proposed. PMID:25821158

  20. Gold(I)-Catalyzed Propargyl Claisen Rearrangement Benjamin D. Sherry and F. Dean Toste*

    E-print Network

    Toste, Dean

    to the oxygen atom,3 and soft Lewis acids, in particular those based on Hg(II) and Pd(II), which catalyze rearrangement can be divided into two classes: hard Lewis acids, which catalyze the reaction by coordination of this reaction has further strengthened its impact.2 In general, Lewis acid catalysis of the Claisen

  1. Enantioselective total synthesis of (-)-nardoaristolone B via a gold(I)-catalyzed oxidative cyclization.

    PubMed

    Homs, Anna; Muratore, Michael E; Echavarren, Antonio M

    2015-02-01

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

  2. 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

  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. Copper-catalyzed cascade reactions of ?,?-unsaturated esters with keto esters

    PubMed Central

    Wang, Chongnian; Li, Zengchang

    2015-01-01

    Summary A copper-catalyzed cascade reaction of ?,?-unsaturated esters with keto esters is reported. It features a copper-catalyzed reductive aldolization followed by a lactonization. This method provides a facile approach to prepare ?-carboxymethyl-?-lactones and ?-carboxymethyl-?-lactones under mild reaction conditions.

  5. Effect of ionic liquids on epoxide hydrolase-catalyzed synthesis of chiral Cinzia Chiappe,*a

    E-print Network

    Hammock, Bruce D.

    Effect of ionic liquids on epoxide hydrolase-catalyzed synthesis of chiral 1,2-diols Cinzia Chiappe Ionic liquids (ILs) offer new possibilities for epoxide hydrolase (EH) catalyzed resolution of epoxides and enantioselective manner in some ionic liquids (ILs),12 although organic solvents (e.g. methyl tert-butyl ether

  6. Substituent Effects of Ligands on Asymmetric Induction in a Prototypical Palladium-Catalyzed Allylation Reaction: Making

    E-print Network

    RajanBabu, T. V. "Babu"

    . Stoichiometric reaction of complexes 10e* and 10j* with the sodium salt of diethyl malonate gave malonate adducts-Catalyzed Allylation Reaction: Making Both Enantiomers of a Product in High Optical Purity Using the Same Source in the palladium-catalyzed asymmetric allylation reaction between 1,3-diphe- nylprop-2-en-1-yl acetate

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

    E-print Network

    He, Chuan

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

  8. Probing the Role of Dynamics in Hydride Transfer Catalyzed by Lactate Dehydrogenase

    E-print Network

    Callender, Robert

    Probing the Role of Dynamics in Hydride Transfer Catalyzed by Lactate Dehydrogenase Nickolay Zhadin, Bronx, New York 10461 ABSTRACT The dynamic nature of the interconversion of pyruvate to lactate as catalyzed by lactate dehydrogenase (LDH) is characterized by laser-induced temperature jump relaxation

  9. 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 ...

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

    PubMed Central

    2015-01-01

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

  11. Enantioselective Synthesis of -Hydroxyenones by Chiral Base-Catalyzed Kornblum DeLaMare Rearrangement

    E-print Network

    Toste, Dean

    are also viable substrates for the base- catalyzed enantioselective reaction. Thus, 23 was converted to 24Enantioselective Synthesis of -Hydroxyenones by Chiral Base-Catalyzed Kornblum De) are important building blocks for asym- metric organic synthesis.1 Enantioselective synthesis of this class

  12. Enantioselective carbonyl-ene reactions catalyzed by chiral cationic dirhodium(II,III) carboxamidates.

    PubMed

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

    2014-12-19

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

  13. Highly Enantioselective Rh-Catalyzed Intramolecular AlderEne Reactions for the

    E-print Network

    Zhang, Xumu

    Highly Enantioselective Rh-Catalyzed Intramolecular Alder±Ene Reactions for the Syntheses of Chiral, the enantioselective processes of metal-catalyzed Alder±ene reactions are relatively unex- plored and the development intramolecular Alder±ene reactions of enynes using a [{Rh(diphos)Cl}2] precursor.[4] Enantioselectivities between

  14. Nickel-catalyzed decarboxylative cross-coupling of perfluorobenzoates with aryl halides and sulfonates.

    PubMed

    Sardzinski, Logan W; Wertjes, William C; Schnaith, Abigail M; Kalyani, Dipannita

    2015-03-01

    A Ni-catalyzed method for the coupling of perfluorobenzoates with aryl halides and pseudohalides is described. Aryl iodides, bromides, chlorides, triflates, and tosylates participate in these transformations to afford the products in good yields. Penta-, tetra-, and trifluorinated biaryl compounds are obtained using these newly developed Ni-catalyzed decarboxylative cross-coupling reactions. PMID:25700128

  15. IONIC LIQUIDS: THE PROSPECTS OF ENZYME-CATALYZED GLYCOSYLATIONS WITHOUT WATER

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Reversing the hydrolytic reaction catalyzed by glycosidases has great potential for the enzyme-catalyzed synthesis of new glycoconjugates. Hydrolysis of glycosidic bonds requires water as a co-reactant, and the reverse reaction (referred to as transglycosylation) is therefore favored by low- or non...

  16. Theoretical Study of Zeolite-Catalyzed Dimethoxymethane Carbonylation to Methyl Methoxyacetate

    E-print Network

    Bell, Alexis

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

  17. 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

  18. 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 ...

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

    E-print Network

    Son, Sunghee

    2008-01-01

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

  20. 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.

  1. Gold-catalyzed tandem reactions of methylenecyclopropanes and vinylidenecyclopropanes.

    PubMed

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

    2014-03-18

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

  2. Semiconductor-catalyzed degradation of phenols with sunlight

    Microsoft Academic Search

    C. Karunakaran; R. Dhanalakshmi

    2008-01-01

    With natural sunlight TiO2 (anatase), Fe2O3, CuO, ZnO, ZnS, ZrO2, CdO, HgO, PbO, PbO2 and Al2O3 catalyze the degradation of phenol but MoO3, Co3O4, CdS, SnO2, Sb2O3, La2O3, CeO2, Sm2O3, Eu2O3, Pb2O3 and Bi2O3 do not. The degradation rates increase linearly with phenol-concentration and area of the catalyst bed but decrease linearly with pH. Air is essential for degradation and

  3. 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

  4. 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.

  5. The palladium-catalyzed trifluoromethylation of aryl chlorides.

    PubMed

    Cho, Eun Jin; Senecal, Todd D; Kinzel, Tom; Zhang, Yong; Watson, Donald A; Buchwald, Stephen L

    2010-06-25

    The trifluoromethyl group can dramatically influence the properties of organic molecules, thereby increasing their applicability as pharmaceuticals, agrochemicals, or building blocks for organic materials. Despite the importance of this substituent, no general method exists for its installment onto functionalized aromatic substrates. Current methods either require the use of harsh reaction conditions or suffer from a limited substrate scope. Here we report the palladium-catalyzed trifluoromethylation of aryl chlorides under mild conditions, allowing the transformation of a wide range of substrates, including heterocycles, in excellent yields. The process tolerates functional groups such as esters, amides, ethers, acetals, nitriles, and tertiary amines and, therefore, should be applicable to late-stage modifications of advanced intermediates. We have also prepared all the putative intermediates in the catalytic cycle and demonstrated their viability in the process. PMID:20576888

  6. The Palladium-Catalyzed Trifluoromethylation of Aryl Chlorides

    PubMed Central

    Cho, Eun Jin; Senecal, Todd D.; Kinzel, Tom; Zhang, Yong; Watson, Donald A.

    2010-01-01

    The trifluoromethyl group can dramatically influence the properties of organic molecules, thereby increasing their applicability as pharmaceuticals, agrochemicals, or building blocks for organic materials. Despite the importance of this substituent, no general method exists for its installment onto functionalized aromatic substrates. Current methods either require the use of harsh reaction conditions or suffer from a limited substrate scope. Herein, we report the palladium-catalyzed trifluoromethylation of aryl chlorides under mild conditions, allowing the transformation of a wide range of substrates, including heterocycles, in excellent yields. The process tolerates functional groups such as esters, amides, ethers, acetals, nitriles, and tertiary amines and therefore should be applicable to late-stage modifications of advanced intermediates. We also have prepared all the putative intermediates in the catalytic cycle and demonstrated their viability in the process. PMID:20576888

  7. Muon-catalyzed D-T fusion at low temperature

    SciTech Connect

    Breunlich, W.H.; Cargnelli, M.; Kammel, P.; Marton, J.; Naegele, N.; Pawlek, P.; Scrinzi, A.; Werner, J.; Zmeskal, J.; Bistirlich, J.; and others

    1987-01-26

    Muon-catalyzed deuterium-tritium fusion was investigated within a wide range of mixtures in liquid and gas (23--35 K) by detection of fusion neutrons. Our improved analysis includes hyperfine effects and allows a clear separation of intrinsic dt sticking ..omega../sub s/ from kinetic effects. Strongly density-dependent cycle rates with values up to 1.45 x 10/sup 8/ s/sup -1/, yields of 113 fusions per muon, and ..omega../sub s/ = (0.45 +- 0.05)% are found. In comparison with previous experiments we confirm that ..omega../sub s/ in liquid is lower than theoretically predicted, but do not find a strong dependence on either c/sub t/ or density.

  8. Amine-catalyzed direct photoarylation of unactivated arenes.

    PubMed

    Zheng, Xingliang; Yang, Luo; Du, Weiyuan; Ding, Aishun; Guo, Hao

    2014-02-01

    Constructing biaryls through direct aromatic C-H functionalization of unactivated arenes has become a popular topic in organic chemistry. Many efficient methods have been developed. In this Communication, a direct arylation of unactivated arenes with a broad range of aryl iodides is reported. This reaction proceeds through a new type of amine-catalyzed single electron transfer initiated radical coupling procedure to form biaryls in high yields under UV irradiation at room temperature. Only 20?mol% of TMEDA is used as the catalyst. No other additives are required for this transformation, thus avoiding the use of toxic transition metal catalysts, strong bases, or large amounts of other organic additives. This greener protocol provides a new strategy to achieve direct aromatic C-H functionalization and offers a new example of cost-effective and environmentally benign access to biaryls. PMID:24288232

  9. Oligonucleotide synthesis catalyzed by the Zn/2+/ ion

    NASA Technical Reports Server (NTRS)

    Sawai, H.; Orgel, L. E.

    1975-01-01

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

  10. Calcium-catalyzed formal [2+2+2] cycloaddition.

    PubMed

    Meyer, Vera J; Ascheberg, Christoph; Niggemann, Meike

    2015-04-20

    A formal intermolecular [2+2+2] cycloaddition reaction of enynes to aldehydes is presented, which can be realized in the presence of a simple and benign calcium catalyst. The reaction proceeds with excellent chemo, regio- and diastereoselectivity and leads to a one-step assembly of highly interesting bicyclic building blocks containing up to three stereocenters from simple precursors via a new type of skeletal rearrangement of enynes. The observed diastereoselectivity is accounted for by two different mechanistic proposals. The first one engages mechanistic prospects arising from a gold catalyzed reaction in the absence of the stabilizing gold substituent. The second proposal involves an unprecedented cyclization-carbonyl allene ene reaction-hydroalkoxylation cascade. PMID:25688729

  11. Laccase-catalyzed oxidative polymerization of phenolic compounds.

    PubMed

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

    2013-12-01

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

  12. Paper microfluidic-based enzyme catalyzed double microreactor.

    PubMed

    Ferrer, Ivonne M; Valadez, Hector; Estala, Lissette; Gomez, Frank A

    2014-08-01

    We describe a paper microfluidic-based enzyme catalyzed double microreactor assay using fluorescent detection. Here, solutions of lactate dehydrogenase (LDH) and diaphorase (DI) were directly spotted onto the microfluidic paper-based analytical device (?PAD). Samples containing lactic acid, resazurin, and nicotinamide adenine dinucleotide oxidized form (NAD(+) ), potassium chloride (KCl), and BSA, in MES buffer were separately spotted onto the ?PAD and MES buffer flowed through the device. A cascade reaction occurs upon the sample spot overlapping with LDH to form pyruvate and nicotinamide adenine dinucleotide reduced form (NADH). Subsequently, NADH is used in the conversion of resazurin to fluorescent resorufin by DI. The ?PAD avoids the need of surface functionalization or enzyme immobilization steps. These microreactor devices are low cost and easy to fabricate and effect reaction based solely on buffer capillary action. PMID:24913741

  13. Water oxidation catalyzed by a dinuclear cobalt-polypyridine complex.

    PubMed

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

    2014-12-22

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

  14. 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

  15. Thermodynamics of formation of carbon nanotubes catalyzed by nickel

    NASA Astrophysics Data System (ADS)

    Jiang, Q.; Wang, Y. W.; Li, J. C.

    1999-11-01

    Thermodynamic size conditions for transitions from a Ni thin film to a Ni particle and then from the Ni particle wrapped with carbon shell to a Ni nanoline are analyzed. It is found that the radius of a transformed particle must be 1.5 times larger than the thickness of the film, and the radius of the formed nanoline have to be larger than half of the radius of the particle. During the above transitions, the wrapped carbon shell on the particle is transformed to a carbon nanotube, which is catalyzed by the shape change of the Ni particle through their semicoherent interface. Since the transition temperature reaches 62% of melting temperature of the Ni thin film, the transitions can proceed kinetically. The above predictions are supported by experimental results.

  16. The pyrite iron cycle catalyzed by Acidithiobacillus ferrooxidans.

    PubMed

    Dumett, Miguel A; Keener, James P

    2014-08-01

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

  17. 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

  18. Acid-catalyzed reactions of epoxides for atmospheric nanoparticle growth.

    PubMed

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

    2014-11-01

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

  19. Electrochemical Investigations into Kinase-Catalyzed Transformations of Tau Protein

    PubMed Central

    2013-01-01

    The formation of neurofibrillary tangles by hyperphosphorylated tau is a well-recognized hallmark of Alzheimer’s disease. Resulting from malfunctioning protein kinases, hyperphosphorylated tau is unable to bind microtubules properly, causing it to self-associate and aggregate. The effects of tau phosphorylation on tau conformation and aggregation are still largely unexplored. The conformational analysis of tau and its hyperphosphorylated forms is usually performed by a variety of spectroscopic techniques, all of which require ample sample concentrations and/or volumes. Here we report on the use of surface based electrochemical techniques that allow for detection of conformational changes and orientation of tau protein as a function of tau phosphorylation by tyrosine and serine/threonine kinases. The electrochemical methods utilize 5?-?-ferrocenyl adenosine triphosphate (Fc-ATP) derivative as a cosubstrate and tau immobilized on gold surface to probe the role of the following protein kinases: Sarcoma related kinase (Src), Abelson tyrosine kinase (Abl), tau-tubulin kinase (TTBK), proto-oncogene tyrosine protein kinase Fyn (Fyn), and glycogen synthase kinase 3-? (Gsk-3?). The single kinase and sequential kinase-catalyzed Fc-phosphorylations modulate the electrochemical signal, pointing to the dramatic changes around the Fc group in the Fc-phosphorylated tau films. The location and orientation of the Fc-group in Fc-tau film was investigated by the surface plasmon resonance based on antiferrocene antibodies. Additional surface characterization of the Fc-tau films by time-of-flight secondary ion-mass spectrometry and X-ray photoelectron spectroscopy revealed that Fc-phosphorylations influence the tau orientation and conformation on surfaces. When Fc-phosphorylations were performed in solution, the subsequently immobilized Fc-tau exhibited similar trends. This study illustrates the validity and the utility of the labeled electrochemical approach for probing the changes in protein film properties, conformation, and orientation as a function of the enzymatically catalyzed modifications. PMID:23687953

  20. Cytochromes P450 catalyze the reduction of ?,?-unsaturated aldehydes.

    PubMed

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

    2011-08-15

    The metabolism of ?,?-unsaturated aldehydes, e.g., 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently, we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O(2), and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ? P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 and rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice a diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and ?-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of the reduction of ?,?-unsaturated aldehydes in the liver. PMID:21766881

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

    PubMed Central

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

    2011-01-01

    The metabolism of ?,?-unsaturated aldehydes, e.g. 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O2, and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ? P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 & rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions, but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and ?-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of reduction of ?,?-unsaturated aldehydes in liver. PMID:21766881

  2. Multimethylation of Rickettsia OmpB catalyzed by lysine methyltransferases.

    PubMed

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

    2014-03-14

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

  3. Electrochemical investigations into kinase-catalyzed transformations of tau protein.

    PubMed

    Rains, Meghan K; Marti?, Sanela; Freeman, Daniel; Kraatz, Heinz Bernhard

    2013-08-21

    The formation of neurofibrillary tangles by hyperphosphorylated tau is a well-recognized hallmark of Alzheimer's disease. Resulting from malfunctioning protein kinases, hyperphosphorylated tau is unable to bind microtubules properly, causing it to self-associate and aggregate. The effects of tau phosphorylation on tau conformation and aggregation are still largely unexplored. The conformational analysis of tau and its hyperphosphorylated forms is usually performed by a variety of spectroscopic techniques, all of which require ample sample concentrations and/or volumes. Here we report on the use of surface based electrochemical techniques that allow for detection of conformational changes and orientation of tau protein as a function of tau phosphorylation by tyrosine and serine/threonine kinases. The electrochemical methods utilize 5'-?-ferrocenyl adenosine triphosphate (Fc-ATP) derivative as a cosubstrate and tau immobilized on gold surface to probe the role of the following protein kinases: Sarcoma related kinase (Src), Abelson tyrosine kinase (Abl), tau-tubulin kinase (TTBK), proto-oncogene tyrosine protein kinase Fyn (Fyn), and glycogen synthase kinase 3-? (Gsk-3?). The single kinase and sequential kinase-catalyzed Fc-phosphorylations modulate the electrochemical signal, pointing to the dramatic changes around the Fc group in the Fc-phosphorylated tau films. The location and orientation of the Fc-group in Fc-tau film was investigated by the surface plasmon resonance based on antiferrocene antibodies. Additional surface characterization of the Fc-tau films by time-of-flight secondary ion-mass spectrometry and X-ray photoelectron spectroscopy revealed that Fc-phosphorylations influence the tau orientation and conformation on surfaces. When Fc-phosphorylations were performed in solution, the subsequently immobilized Fc-tau exhibited similar trends. This study illustrates the validity and the utility of the labeled electrochemical approach for probing the changes in protein film properties, conformation, and orientation as a function of the enzymatically catalyzed modifications. PMID:23687953

  4. Vanadium bromoperoxidase-catalyzed biosynthesis of halogenated marine natural products.

    PubMed

    Carter-Franklin, Jayme N; Butler, Alison

    2004-11-24

    Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products. The biogenesis of the cyclic halogenated terpene marine natural products, in particular, has attracted sustained interest in part because terpenes are the biogenic precursors of many bioactive metabolites. The first enzymatic asymmetric bromination and cyclization of a terpene, producing marine natural products isolated from red algae, is reported. Vanadium bromoperoxidase (V-BrPO) isolated from marine red algae (species of Laurencia, Plocamium, Corallina) catalyzes the bromination of the sesquiterpene (E)-(+)-nerolidol producing alpha-, beta-, and gamma-snyderol and (+)-3beta-bromo-8-epicaparrapi oxide. alpha-Snyderol, beta-snyderol, and (+)-3beta-bromo-8-epicaparrapi oxide have been isolated from Laurencia obtusa, and each have also been isolated from other species of marine red algae. gamma-Snyderol is a proposed intermediate in other bicyclo natural products. Single diastereomers of beta-snyderol, gamma-snyderol, and mixed diastereomers of (+)-3beta-bromo-8-epicaparrapi oxide (de = 20-25%) are produced in the enzyme reaction, whereas two diastereomers of these compounds are formed in the synthesis with 2,4,4,6-tetrabromocyclohexa-2,5-dienone (TBCO). V-BrPO likely functions by catalyzing the two-electron oxidation of bromide ion by hydrogen peroxide producing a bromonium ion or equivalent in the active site that brominates one face of the terminal olefin of nerolidol. These results establish V-BrPO's role in the biosynthesis of brominated cyclic sesquiterpene structures from marine red algae for the first time. PMID:15548002

  5. [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

  6. The Mechanism of the Rhodium(I)-Catalyzed [2 + 2 + 1] Carbocyclization Reaction of Dienes and CO: A

    E-print Network

    Baik, Mu-Hyun

    The Mechanism of the Rhodium(I)-Catalyzed [2 + 2 + 1] Carbocyclization Reaction of Dienes and CO-mail: mbaik@indiana.edu Abstract: The rhodium(I) catalyzed [2 + 2 + 1] carbocyclization of tethered diene rhodium(I)-catalyzed [2 + 2 + 1] carbocyclization. One of the apparent requirements for the [2 + 2 + 1

  7. New metal catalyzed syntheses of nanostructured boron nitride and alkenyldecaboranes

    NASA Astrophysics Data System (ADS)

    Chatterjee, Shahana

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

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

    NASA Astrophysics Data System (ADS)

    Honda, Kazuhiro; Ohdaira, Keisuke; Matsumura, Hideki

    2008-05-01

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

  9. Pd-Catalyzed ?-Arylation of ?,?-Difluoroketones with Aryl Bromides and Chlorides. A Route to Difluoromethylarenes

    PubMed Central

    2015-01-01

    We report the Pd-catalyzed ?-arylation of ?,?-difluoroketones with aryl and heteroaryl bromides and chlorides catalyzed by an air- and moisture-stable palladacyclic complex containing P(t-Bu)Cy2 as ligand. The combination of this Pd-catalyzed arylation and base-induced cleavage of the acyl–aryl C–C bond within the ?-aryl-?,?-difluoroketone constitutes a one-pot, two-step procedure to synthesize difluoromethylarenes from aryl halides. A broad range of electronically varied aryl and heteroaryl bromides and chlorides underwent these two transformations, providing ?-aryl-?,?-difluoroketones, difluoromethylarenes, and difluoromethylheteroarenes in high yields. PMID:24588379

  10. Structural Analysis of ATP Analogs Compatible with Kinase-Catalyzed Labeling

    PubMed Central

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

    2012-01-01

    Kinase-catalyzed protein phosphorylation is an important biochemical process involved in cellular functions. We recently discovered that kinases promiscuously accept ?-modified ATP analogs as cosubstrates and used several ATP analogs as tools for studying protein phosphorylation. Herein, we explore the structural requirements of ?-modified ATP analogs for kinase compatibility. To understand the influence of linker length and composition, a series of ATP analogs was synthesized and the efficiency of kinase-catalyzed labeling was determined by quantitative mass spectrometry. This study on factors influencing kinase cosubstrate promiscuity will enable design of ATP analogs for a variety of kinase-catalyzed labeling reactions. PMID:23116557

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

    NASA Astrophysics Data System (ADS)

    Hoang, Tony Phuc

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

  12. DFT study of the molybdenum-catalyzed deoxydehydration of vicinal diols.

    PubMed

    Lupp, Daniel; Christensen, Niels Johan; Dethlefsen, Johannes R; Fristrup, Peter

    2015-02-16

    The mechanism of the molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols has been investigated using density functional theory. The proposed catalytic cycle involves condensation of the diol with an Mo(VI) oxo complex, oxidative cleavage of the diol resulting in an Mo(IV) complex, and extrusion of the alkene. We have compared the proposed pathway with several alternatives, and the results have been corroborated by comparison with the molybdenum-catalyzed sulfoxide reduction recently published by Sanz et?al. and with experimental observations for the DODH itself. Improved understanding of the mechanism should expedite future optimization of molybdenum-catalyzed biomass transformations. PMID:25588805

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

    PubMed

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

    2014-06-10

    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

  14. 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

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

    SciTech Connect

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

    2008-07-29

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

  16. Recent advances in osmium-catalyzed hydrogenation and dehydrogenation reactions.

    PubMed

    Chelucci, Giorgio; Baldino, Salvatore; Baratta, Walter

    2015-02-17

    Conspectus A current issue in metal-catalyzed reactions is the search for highly efficient transition-metal complexes affording high productivity and selectivity in a variety of processes. Moreover, there is also a great interest in multitasking catalysts that are able to efficiently promote different organic transformations by careful switching of the reaction parameters, such as temperature, solvent, and cocatalyst. In this context, osmium complexes have shown the ability to catalyze efficiently different types of reactions involving hydrogen, proving at the same time high thermal stability and simple synthesis. In the catalytic reduction of C?X (X = O, N) bonds by both hydrogenation (HY) and transfer hydrogenation (TH) reactions, the most interest has been focused on homogeneous systems based on rhodium, iridium, and in particular ruthenium catalysts, which have proved to catalyze chemo- and stereoselective hydrogenations with remarkable efficiency. By contrast, osmium catalysts have received much less attention because they are considered less active on account of their slower ligand exchange kinetics. Thus, this area remained almost neglected until recent studies refuted these prejudices. The aim of this Account is to highlight the impressive developments achieved over the past few years by our and other groups on the design of new classes of osmium complexes and their applications in homogeneous catalytic reactions involving the hydrogenation of carbon-oxygen and carbon-nitrogen bonds by both HY and TH reactions as well as in alcohol deydrogenation (DHY) reactions. The work described in this Account demonstrates that osmium complexes are emerging as powerful catalysts for asymmetric and non-asymmetric syntheses, showing a remarkably high catalytic activity in HY and TH reactions of ketones, aldehydes, imines, and esters as well in DHY reactions of alcohols. Thus, for instance, the introduction of ligands with an NH function, possibly in combination with a pyridine ring, led to a new family of [OsCl2(PP)(NN)] (NN = diamine, 2-aminomethylpyridine; PP = diphosphine) and pincer [OsCl(CNN)(PP)] (HCNN = 6-aryl-2-aminomethylpyridine, 2-aminomethylbenzo[h]quinoline) complexes, which are outstanding catalysts for (asymmetric) HY and TH of carbonyl compounds and DHY of alcohols with turnover numbers and turnover frequencies up to 10(5) and 10(6) h(-1), respectively. In addition, PNN osmium complexes containing the 2-aminomethylpyridine motif have been found to be among the most active catalysts for HY of esters. These complexes have shown catalytic activities that are comparable and in some cases superior to those reported for analogous ruthenium systems. These results give an idea of the potential of Os complexes for the design of new highly productive and robust catalysts for the synthesis of chiral and nonchiral alcohols and amines as well as ketones from alcohols. Thus, we hope that this report will promote increased interest in the chemistry of these metal complexes, opening novel opportunities for new catalytic processes as well as the improvement of existing ones. PMID:25650714

  17. High power density yeast catalyzed microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Ganguli, Rahul

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

  18. Bonding by Hydroxide-Catalyzed Hydration and Dehydration

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung

    2008-01-01

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

  19. Highly selective asymmetric Rh-catalyzed hydroformylation of heterocyclic olefins.

    PubMed

    Chikkali, Samir H; Bellini, Rosalba; de Bruin, Bas; van der Vlugt, Jarl Ivar; Reek, Joost N H

    2012-04-18

    A small family of new chiral hybrid, diphosphorus ligands, consisting of phosphine-phosphoramidites L1 and L2 and phosphine-phosphonites L3a-c, was synthesized for the application in Rh-catalyzed asymmetric hydroformylation of heterocyclic olefins. High-pressure (HP)-NMR and HP-IR spectroscopy under 5-10 bar of syngas has been employed to characterize the corresponding catalyst resting state with each ligand. Indole-based ligands L1 and L2 led to selective ea coordination, while the xanthene derived system L3c gave predominant ee coordination. Application of the small bite-angle ligands L1 and L2 in the highly selective asymmetric hydroformylation (AHF) of the challenging substrate 2,3-dihydrofuran (1) yielded the 2-carbaldehyde (3) as the major regioisomer in up to 68% yield (with ligand L2) along with good ee's of up to 62%. This is the first example in which the asymmetric hydroformylation of 1 is both regio- and enantioselective for isomer 3. Interestingly, use of ligand L3c in the same reaction completely changed the regioselectivity to 3-carbaldehyde (4) with a remarkably high enantioselectivity of 91%. Ligand L3c also performs very well in the Rh-catalyzed asymmetric hydroformylation of other heterocyclic olefins. Highly enantioselective conversion of the notoriously difficult substrate 2,5-dihydrofuran (2) is achieved using the same catalyst, with up to 91% ee, concomitant with complete regioselectivity to the 3-carbaldehyde product (4) under mild reaction conditions. Interestingly, the Rh-catalyst derived from L3c is thus able to produce both enantiomers of 3-carbaldehyde 4, simply by changing the substrate from 1 to 2. Furthermore, 85% ee was obtained in the hydroformylation of N-acetyl-3-pyrroline (5) with exceptionally high regioselectivities for 3-carbaldehyde 8Ac (>99%). Similarly, an ee of 86% for derivative 8Boc was accomplished using the same catalyst system in the AHF of N-(tert-butoxycarbonyl)-3-pyrroline (6). These results represent the highest ee's reported to date in the AHF of dihydrofurans (1, 2) and 3-pyrrolines (5, 6). PMID:22424099

  20. 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.

  1. Exploring chain length selectivity in HIC-catalyzed polycondensation reactions.

    PubMed

    Feder, David; Gross, Richard A

    2010-03-01

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

  2. Enantioselective Rhodium-Catalyzed Addition of Potassium Alkenyltrifluoroborates to Cyclic Imines 

    E-print Network

    Luo, Yunfei; Carnell, Andrew J.; Lam, Hon Wai

    2012-07-02

    Cyclic imines, in which the C[DOUBLE BOND]N bond is constrained in the Z?geometry, have been identified as highly effective substrates for enantioselective rhodium-catalyzed additions of potassium alkenyltrifluoroborates. Not only is the alkene...

  3. 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...

  4. 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. ...

  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. Formal total synthesis of (-)-taxol through Pd-catalyzed eight-membered carbocyclic ring formation.

    PubMed

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

    2015-01-01

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

  7. 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)

  8. Synthesis of 5,5-Disubstituted Butenolides Based on a Pd-Catalyzed ?-Arylation Strategy

    E-print Network

    Hyde, Alan M.

    Methods for the construction of quaternary carbon centers are of great interest to synthetic chemists due to their presence in natural products. Development of the Pd-catalyzed arylation of butenolides with high selectivity ...

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

    EPA Science Inventory

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

  10. OXIDATIVE 4-DECHLORINATION OF POLYCHLORINATED PHENOLS IS CATALYZED BY EXTRACELLULAR FUNGAL LIGNIN PEROXIDASES (JOURNAL VERSION)

    EPA Science Inventory

    The extracellular lignin peroxidases (ligninases) of Phanerochaete chrysosporium catalyzed H2O2-dependent spectral changes in several environmentally significant polychlorinated phenols: 2,4-dichloro-,2,4,5-trichloro-, and pentachlorophenol. Gas chromatography/mass spectrometry s...

  11. DOI:10.1002/ejic.201300710 Reaction Mechanism of Water Oxidation Catalyzed by

    E-print Network

    Liao, Rongzhen

    to the opening of the benzene ring, which explains the observation of fast catalyst degrada- tion. The lack a quite fast catalyst degradation. Kinetic studies also sug- gest that the formation of O2 catalyzed

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

    PubMed Central

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

    2013-01-01

    Arylboronic acids are gaining increased importance as reagents and target structures in a variety of useful applications. Recently, the palladium-catalyzed synthesis of arylboronic acids employing the atom economical tetrahydroxydiboron (BBA) reagent has been reported. The high cost associated with palladium, combined with several limitations of both palladium and copper-catalyzed processes, prompted us to develop an alternative method. Thus, the nickel-catalyzed borylation of aryl and heteroaryl halides and pseudo-halides using tetrahydroxydiboron (BBA) has been formulated. The reaction proved to be widely functional group tolerant and applicable to a number of heterocyclic systems. To the best of our knowledge, the examples presented here represent the only effective Ni-catalyzed Miyaura borylations conducted at room temperature. PMID:23777538

  13. 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 ...

  14. Mechanistic Studies on the Copper-Catalyzed N-Arylation of Amides

    E-print Network

    Strieter, Eric R.

    The copper-catalyzed N-arylation of amides, i.e., the Goldberg reaction, is an efficient method for the construction of products relevant to both industry and academic settings. Herein, we present mechanistic details ...

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

    EPA Science Inventory

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

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

    E-print Network

    Hyde, Alan M. (Alan Michael)

    2009-01-01

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

  17. 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 ...

  18. 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 ...

  19. Iodine-catalyzed regioselective 2-sulfonylation of indoles with sodium sulfinates.

    PubMed

    Xiao, Fuhong; Chen, Hui; Xie, Hao; Chen, Shuqing; Yang, Luo; Deng, Guo-Jun

    2014-01-01

    Iodine-catalyzed selective 2-arylsulfonyl indole formation from indoles and sodium sulfinates is disclosed. Various substituted 2-arylsulfonyl indoles were obtained in one pot in the absence of metal catalyst at room temperature under air. PMID:24328422

  20. 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 ...

  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. Mechanism and Transition-State Structures for Nickel-Catalyzed Reductive Alkyne?Aldehyde Coupling Reactions

    E-print Network

    McCarren, P. R.

    The mechanism of nickel-catalyzed reductive alkyne?aldehyde coupling reactions has been investigated using density functional theory. The preferred mechanism involves oxidative cyclization to form the nickeladihydrofuran ...

  3. Helix Stabilization Precedes Aqueous and Bilayer-Catalyzed Fiber Formation in Islet

    E-print Network

    Miranker, Andrew

    Helix Stabilization Precedes Aqueous and Bilayer-Catalyzed Fiber Formation in Islet Amyloid, all--strand amyloid fiber. Although predominantly disordered, IAPP transiently samples -helical structures, yet all assemble into a common, highly ordered filamentous structure. Amyloid fiber structure

  4. An efficient route to highly strained cyclobutenes: indium-catalyzed reactions of enynals with alkynes.

    PubMed

    Liang, Renxiao; Jiang, Huanfeng; Zhu, Shifa

    2015-03-12

    A catalytic method to synthesize the highly strained cyclobutene was developed. The reaction was believed to proceed through a formal indium-catalyzed [2+2] cycloaddition between electron-deficient enynals and various alkynes. PMID:25578629

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

    E-print Network

    Dussault, Daemian David, 1973-

    2005-01-01

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

  6. 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 ...

  7. 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 ...

  8. Enantioselective Rhodium-Catalyzed Nucleophilic Allylation of Cyclic Imines with Allylboron Reagents 

    E-print Network

    Luo, Yunfei; Hepburn, Hamish B.; Chotsaeng, Nawasit; Lam, Hon Wai

    The highly diastereo- and enantioselective title reaction of a range of cyclic imines with various potassium allyltrifluoroborates most likely proceeds via allylrhodium(I) intermediates, and represents the first rhodium-catalyzed enantioselective...

  9. Highly enantioselective hydroformylation of dihydrofurans catalyzed by hybrid phosphine-phosphonite rhodium complexes.

    PubMed

    Chikkali, Samir H; Bellini, Rosalba; Berthon-Gelloz, Guillaume; van der Vlugt, Jarl Ivar; de Bruin, Bas; Reek, Joost N H

    2010-02-28

    Unprecedented regio- and enantioselectivities (>91%) are reported for the Rh-catalyzed asymmetric hydroformylation of 2,3- and 2,5-dihydrofuran using tunable hybrid phosphine-phosphonite ligands. PMID:20449264

  10. Progress in nucleophilic catalysis and development of nickel-catalyzed cross-couplings of propargylic halides

    E-print Network

    Smith, Sean W. (Sean Wesley)

    2009-01-01

    Chapter 1 describes the development of two organocatalytic processes. The first is a 13-alkylation reaction of Michael acceptors, and represents a novel umpolung process catalyzed by N-heterocyclic carbenes. The second ...

  11. 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 ...

  12. Nickel-catalyzed reaction of thioisatins and alkynes: a facile synthesis of thiochromones.

    PubMed

    Inami, Tasuku; Kurahashi, Takuya; Matsubara, Seijiro

    2014-11-01

    A new synthetic method for thiochromones was developed by using nickel-catalyzed decarbonylative cycloaddition of readily available thioisatins with alkynes. This reaction proceeded under very mild conditions and has quite high functional group compatibility. PMID:25347619

  13. Palladium-catalyzed substitution of (coumarinyl)methyl acetates with C-, N-, and S-nucleophiles

    E-print Network

    Chattopadhyay, Kalicharan; Fenster, Erik; Grenning, Alexander James; Tunge, Jon A.

    2012-07-27

    The palladium-catalyzed nucleophilic substitution of (coumarinyl)methyl acetates is described. The reaction proceeds though a palladium ?-benzyl-like complex and allows for many different types of C-, N-, and S-nucleophiles ...

  14. Synthesis of Aryl Sulfonamides via Palladium-Catalyzed Chlorosulfonylation of Arylboronic Acids

    E-print Network

    Niljianskul, Nootaree

    A palladium-catalyzed method for the preparation of sulfonamides is described. The process exhibits significant functional group tolerance and allows for the preparation of a number of arylsulfonyl chlorides and sulfonamides ...

  15. Palladium-Catalyzed Conversion of Aryl and Vinyl Triflates to Bromides and Chlorides

    E-print Network

    Shen, Xiaoqiang

    2010-01-01

    The palladium-catalyzed conversion of aryl and vinyl triflates to aryl and vinyl halides (bromides and chlorides) has been developed using dialkylbiaryl phosphine ligands. A variety of aryl, heteroaryl, and vinyl halides ...

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

    E-print Network

    Teverovskiy, Georgiy

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

  17. Periodic current oscillation catalyzed by ?-MnO2 nanosheets.

    PubMed

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

    2015-01-12

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

  18. Feasibility of an antiproton catalyzed fission fragment rocket

    SciTech Connect

    Hdinger, D.S.

    1992-03-01

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

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

    PubMed

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

    2014-07-15

    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. Micellar nanoreactors for hematin catalyzed synthesis of electrically conducting polypyrrole.

    PubMed

    Ravichandran, Sethumadhavan; Nagarajan, Subhalakshmi; Kokil, Akshay; Ponrathnam, Timothy; Bouldin, Ryan M; Bruno, Ferdinando F; Samuelson, Lynne; Kumar, Jayant; Nagarajan, Ramaswamy

    2012-09-18

    Enzymatic synthesis of doped polypyrrole (PPy) complexes using oxidoreductases (specifically peroxidases) is very well established "green" methods for producing conducting polypyrrole. The importance of this approach is realized by the numerous potential opportunities of using PPy in biological applications. However, due to very high costs and low acid stability of these enzymes, there is need for more robust alternate biomimetic catalysts. Hematin, a hydroxyferriprotoporphyrin, has a similar iron catalytic active center like the peroxidases and has previously shown to catalyze polymerization of phenol monomers at pH 12. The insolubility of hematin due to extensive self-aggregation at low pH conditions has prevented its use in the synthesis of conjugated polymers. In this study, we have demonstrated the use of a micellar environment with sodium dodecylbenzenesulfonate (DBSA) for biomimetic synthesis of PPy. The micellar environment helps solubilize hematin, generating nanometer size reactors for the polymerization of pyrrole. The resulting PPy is characterized using UV-visible, Fourier transform infrared, and X-ray photoelectron spectroscopy and reveals the formation of an ordered PPy/DBSA complex with conductivities approaching 0.1 S/cm. PMID:22906396

  1. Theoretical study on the BF3-catalyzed Meinwald rearrangement reaction.

    PubMed

    Fraile, José María; Mayoral, José Antonio; Salvatella, Luis

    2014-07-01

    The mechanisms of the BF3-catalyzed Meinwald rearrangement reactions of five epoxides in dichloromethane solution have been studied at the M062X/6-311++G(2df,2pd) level. Accordingly, the Lewis acid-epoxide complex can react through several alternative pathways, though three phases (ring opening, C-C bond rotation, and hydrogen or alkyl group migration) are required in any path. In some cases, a concerted pathway (involving all three successive phases) is found. Otherwise, the reaction takes place through a reaction mechanism involving a zwitterion or a BF3 addition compound (formed by fluoride transfer from the BF3 moiety to the incipient carbocationic center generated by C-O bond rupture) or both as reaction intermediate(s). The BF2-bound fluorohydrin yields the reaction product through a concerted process involving fluoride transfer from the C-F bond to the OBF2 group and hydrogen or alkyl group migration, as first demonstrated in this work. Effects of a number of features (solvent effects, concurrent hydrogen/alkyl group migration, carbocation substitution, benzylic conjugation) are also discussed. PMID:24893807

  2. 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

  3. 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.

  4. Broadening the scope of glycosyltransferase-catalyzed sugar nucleotide synthesis

    PubMed Central

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

    2013-01-01

    We described the integration of the general reversibility of glycosyltransferase-catalyzed reactions, artificial glycosyl donors, and a high throughput colorimetric screen to enable the engineering of glycosyltransferases for combinatorial sugar nucleotide synthesis. The best engineered catalyst from this study, the OleD Loki variant, contained the mutations P67T/I112P/T113M/S132F/A242I compared with the OleD wild-type sequence. Evaluated against the parental sequence OleD TDP16 variant used for screening, the OleD Loki variant displayed maximum improvements in kcat/Km of >400-fold and >15-fold for formation of NDP–glucoses and UDP–sugars, respectively. This OleD Loki variant also demonstrated efficient turnover with five variant NDP acceptors and six variant 2-chloro-4-nitrophenyl glycoside donors to produce 30 distinct NDP–sugars. This study highlights a convenient strategy to rapidly optimize glycosyltransferase catalysts for the synthesis of complex sugar nucleotides and the practical synthesis of a unique set of sugar nucleotides. PMID:23610417

  5. 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.

  6. 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.

  7. Process Intensification in Base-Catalyzed Biodiesel Production

    SciTech Connect

    McFarlane, Joanna [ORNL] [ORNL; Birdwell Jr, Joseph F [ORNL] [ORNL; Tsouris, Costas [ORNL] [ORNL; Jennings, Hal L [ORNL] [ORNL

    2008-01-01

    Biodiesel is considered a means to diversify our supply of transportation fuel, addressing the goal of reducing our dependence on oil. Recent interest has resulted in biodiesel manufacture becoming more widely undertaken by commercial enterprises that are interested in minimizing the cost of feedstock materials and waste production, as well as maximizing the efficiency of production. Various means to accelerate batch processing have been investigated. Oak Ridge National Laboratory has experience in developing process intensification methods for nuclear separations, and this paper will discuss how technologies developed for very different applications have been modified for continuous reaction/separation of biodiesel. In collaboration with an industrial partner, this work addresses the aspect of base-catalyzed biodiesel production that limits it to a slow batch process. In particular, we have found that interfacial mass transfer and phase separation control the transesterification process and have developed a continuous two-phase reactor for online production of a methyl ester and glycerol. Enhancing the mass transfer has additional benefits such as being able to use an alcohol-to-oil phase ratio closer to stoichiometric than in conventional processing, hence minimizing the amount of solvent that has to be recycled and reducing post-processing clean up costs. Various technical issues associated with the application of process intensification technology will be discussed, including scale-up from the laboratory to a pilot-scale undertaking.

  8. Temperature dependences of rate coefficients for electron catalyzed mutual neutralization

    SciTech Connect

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

    2011-07-14

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

  9. 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.

  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. Hydrolysis of cellulose catalyzed by novel acidic ionic liquids.

    PubMed

    Zhuo, Kelei; Du, Quanzhou; Bai, Guangyue; Wang, Congyue; Chen, Yujuan; Wang, Jianji

    2015-01-22

    The conversion of cellulosic biomass directly into valuable chemicals becomes a hot subject. Six novel acidic ionic liquids (ILs) based on 2-phenyl-2-imidazoline were synthesized and characterized by UV-VIS, TGA, and NMR. The novel acidic ionic liquids were investigated as catalysts for the hydrolysis of cellulose in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). The acidic ionic liquids with anions HSO4(-) and Cl(-) showed better catalytic performance for the hydrolysis of cellulose than those with H2PO4(-). The temperature and dosage of water affect significantly the yield of total reducing sugar (TRS). When the hydrolysis of cellulose was catalyzed by 1-propyl sulfonic acid-2-phenyl imidazoline hydrogensulfate (IL-1) and the dosage of water was 0.2g, the TRS yield was up to 85.1% within 60 min at 100°C. These new acidic ionic liquids catalysts are expected to have a wide application in the conversion of cellulose into valuable chemicals. PMID:25439867

  12. Computational model of membrane fission catalyzed by ESCRT-III.

    PubMed

    Fabrikant, Gur; Lata, Suman; Riches, James D; Briggs, John A G; Weissenhorn, Winfried; Kozlov, Michael M

    2009-11-01

    ESCRT-III proteins catalyze membrane fission during multi vesicular body biogenesis, budding of some enveloped viruses and cell division. We suggest and analyze a novel mechanism of membrane fission by the mammalian ESCRT-III subunits CHMP2 and CHMP3. We propose that the CHMP2-CHMP3 complexes self-assemble into hemi-spherical dome-like structures within the necks of the initial membrane buds generated by CHMP4 filaments. The dome formation is accompanied by the membrane attachment to the dome surface, which drives narrowing of the membrane neck and accumulation of the elastic stresses leading, ultimately, to the neck fission. Based on the bending elastic model of lipid bilayers, we determine the degree of the membrane attachment to the dome enabling the neck fission and compute the required values of the protein-membrane binding energy. We estimate the feasible values of this energy and predict a high efficiency for the CHMP2-CHMP3 complexes in mediating membrane fission. We support the computational model by electron tomography imaging of CHMP2-CHMP3 assemblies in vitro. We predict a high efficiency for the CHMP2-CHMP3 complexes in mediating membrane fission. PMID:19936052

  13. Computational Model of Membrane Fission Catalyzed by ESCRT-III

    PubMed Central

    Fabrikant, Gur; Lata, Suman; Riches, James D.; Briggs, John A. G.; Weissenhorn, Winfried; Kozlov, Michael M.

    2009-01-01

    ESCRT-III proteins catalyze membrane fission during multi vesicular body biogenesis, budding of some enveloped viruses and cell division. We suggest and analyze a novel mechanism of membrane fission by the mammalian ESCRT-III subunits CHMP2 and CHMP3. We propose that the CHMP2-CHMP3 complexes self-assemble into hemi-spherical dome-like structures within the necks of the initial membrane buds generated by CHMP4 filaments. The dome formation is accompanied by the membrane attachment to the dome surface, which drives narrowing of the membrane neck and accumulation of the elastic stresses leading, ultimately, to the neck fission. Based on the bending elastic model of lipid bilayers, we determine the degree of the membrane attachment to the dome enabling the neck fission and compute the required values of the protein-membrane binding energy. We estimate the feasible values of this energy and predict a high efficiency for the CHMP2-CHMP3 complexes in mediating membrane fission. We support the computational model by electron tomography imaging of CHMP2-CHMP3 assemblies in vitro. We predict a high efficiency for the CHMP2-CHMP3 complexes in mediating membrane fission. PMID:19936052

  14. 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

  15. New cardiolipin analogs synthesized by phospholipase D-catalyzed transphosphatidylation.

    PubMed

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

    2012-10-01

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

  16. On Transition Metal Catalyzed Reduction of N-nitrosodimethlamine

    E-print Network

    Zhou, Jun; Tian, Junhua; Zhao, Zhun

    2014-01-01

    This report provides a critical review on "Metal-Catalyzed Reduction of N-Nitrosodimethylamine with Hydrogen in Water", by Davie et al. N-nitrosodimethlamine (NDMA) is a contaminant in drinking and ground water which is difficult to remove by conventional physical methods, such as air stripping. Based on the reported robust capability of metal based powder shaped catalysts in hydrogen reduction, several monometallic and bimetallic catalyst are studied in this paper on the reduction of NDMA with hydrogen. Two kinds of kinetics, metal weight normalized and surface area normalized, are compared between each catalyst in terms of pseudo-first order reaction rate. Palladium, copper enhanced palladium and nickel are found to be very efficient in NDMA reduction, with half-lives on the order of hours per 10 mg/l catalyst metal. Preliminary LC-MS data and carbon balance showed no intermediates. Finally, a simple hydrogen and NMDA surface activated reaction mechanism is proposed by the author for palladium and nickel.

  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. Energetic communication between mitochondria and nucleus directed by catalyzed phosphotransfer

    PubMed Central

    Dzeja, Petras P.; Bortolon, Ryan; Perez-Terzic, Carmen; Holmuhamedov, Ekshon L.; Terzic, Andre

    2002-01-01

    Exchange of information between the nucleus and cytosol depends on the metabolic state of the cell, yet the energy-supply pathways to the nuclear compartment are unknown. Here, the energetics of nucleocytoplasmic communication was determined by imaging import of a constitutive nuclear protein histone H1. Translocation of H1 through nuclear pores in cardiac cells relied on ATP supplied by mitochondrial oxidative phosphorylation, but not by glycolysis. Although mitochondria clustered around the nucleus, reducing the distance for energy transfer, simple nucleotide diffusion was insufficient to meet the energetic demands of nuclear transport. Rather, the integrated phosphotransfer network was required for delivery of high-energy phosphoryls from mitochondria to the nucleus. In neonatal cardiomyocytes with low creatine kinase activity, inhibition of adenylate kinase-catalyzed phosphotransfer abolished nuclear import. With deficient adenylate kinase, nucleoside diphosphate kinase, which secures phosphoryl exchange between ATP and GTP, was unable to sustain nuclear import. Up-regulation of creatine kinase phosphotransfer, to mimic metabolic conditions of adult cardiac cells, rescued H1 import, suggesting a developmental plasticity of the cellular energetic system. Thus, mitochondrial oxidative phosphorylation coupled with phosphotransfer relays provides an efficient energetic unit in support of nuclear transport. PMID:12119406

  19. ATP-Independent Hydrocarbon Formation Catalyzed by Isolated Nitrogenase Cofactors

    PubMed Central

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

    2012-01-01

    Nitrogenase is a highly complex and uniquely versatile metalloenzyme that is capable of reducing a broad spectrum of substrates, such as dinitrogen (N2), carbon monoxide (CO) and cyanide (CN-), under ambient conditions.[1-4] The molybdenum (Mo)- and vanadium (V)-nitrogenases are two homologous members of this enzyme family, both utilizing a specific reductase (Fe protein) to donate electrons to the cofactor site (FeMoco or FeVco) of a catalytic component (MoFe or VFe protein) during catalysis. The buried location of cofactor poses a challenge to electron transfer in this process, rendering it strictly dependent on ATP-assisted formation of an electron transport chain—within a complex between the reductase and the catalytic component—that extends all the way from the [Fe4S4] cluster of the former, via the P-cluster, to the cofactor site of the latter.[5] On the other hand, both FeMoco and FeVco can be extracted as intact entities into organic solvents,[6-8] spurring interest in seeking an ATP-independent reaction system, in which electrons can be directly delivered to the isolated cofactors for substrate reduction. In particular, the recent discovery that nitrogenases can reduce CO to hydrocarbons[3,4] makes it an attractive task to explore the capacity of cofactors to directly catalyze the formation of hydrocarbons from CO, as well as CN-—another carbonaceous molecule that is isoelectronic to CO. PMID:22253035

  20. Clay-catalyzed reactions of coagulant polymers during water chlorination

    USGS Publications Warehouse

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

    2004-01-01

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

  1. Forced Muon Catalyzed Fusion in Heterogeneous Layers of Hydrogen Isotopes

    NASA Astrophysics Data System (ADS)

    Eskandari, M. R.; Gheisari, R.

    Muon cycling dynamics for muon catalyzed fusion in heterogeneous solid layers are considered through decay of complex molecule [(dt? ){? , J}* dee]{v, k}. The suggested fusion system consists of three layers which are alternatively repeated. The first layer is D/T (deuterium, tritium) which provides [(dt? ){? , J}* dee]{v, k} molecules. The second layer is T2 molecules which are used to slow down the muonic atoms and the third layer is D2 molecules. The design is in a way in which dt?, muonic deuterium and tritium molecules, are produced in resonance. It is shown, by considering muonic dynamics theoretically in a suggested heterogeneous system and determining its cycling rate by using a more advanced calculational method, that for equal deuterium, tritium concentration (Cd=Ct=0.5) in D/T layer and ?'=?0=?=1 (relative density for each layer respectively and given in liquid hydrogen density LHD=4.25×1022cm-3), the muon cycling rate is optimum for the suggested heterogeneous system and has 15% enhancement with respect to the conventional D/T system. It is also shown that for ?0<0.0003 the muon cycling rate in D2 is almost stopped, and for ?0?1 muon cycling rate increases, but this is not recommended due to low and costly tritium availability.

  2. Primordial Lithium Abundance in Catalyzed Big Bang Nucleosynthesis

    E-print Network

    Chris Bird; Kristen Koopmans; Maxim Pospelov

    2008-05-19

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

  3. 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

  4. 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.

  5. Molecular mechanisms of cobalt-catalyzed hydrogen evolution

    PubMed Central

    Marinescu, Smaranda C.; Winkler, Jay R.; Gray, Harry B.

    2012-01-01

    Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV/Co. Protonation of CoI produces a transient CoIII-H complex that was characterized by nuclear magnetic resonance spectroscopy. The CoIII-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that CoIII-H produces hydrogen by two competing pathways: a slower homolytic route involving two CoIII-H species and a dominant heterolytic channel in which a highly reactive CoII-H transient is generated by CoI reduction of CoIII-H. PMID:22949704

  6. MEMS-Based Satellite Micropropulsion Via Catalyzed Hydrogen Peroxide Decomposition

    NASA Technical Reports Server (NTRS)

    Hitt, Darren L.; Zakrzwski, Charles M.; Thomas, Michael A.; Bauer, Frank H. (Technical Monitor)

    2001-01-01

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

  7. 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

  8. Nitrite increases the enantioselectivity of sulfoxidation catalyzed by myoglobin derivatives in the presence of hydrogen peroxide

    Microsoft Academic Search

    Vincenza Pironti; Stefania Nicolis; Enrico Monzani; Stefano Colonna; Luigi Casella

    2004-01-01

    The effect of nitrite in the sulfoxidation of organic sulfides catalyzed by myoglobin (Mb) in the presence of hydrogen peroxide has been investigated. A general improvement in enantioselectivity was found for the reaction catalyzed by horse heart metMb and a series of sperm whale metMb derivatives including the wild type protein, the active site mutants T67K Mb, T67R Mb, T67R\\/S92D

  9. 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

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

    PubMed Central

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

    2013-01-01

    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

  11. Transition-Metal-Catalyzed Denitrogenative Transannulation: Converting Triazoles into Other Heterocyclic Systems

    PubMed Central

    Chattopadhyay, Buddhadeb

    2012-01-01

    Transition metal catalyzed denitrogenative transannulation of a triazole ring has recently received considerable attention as a new concept for the construction of diverse nitrogen-containing heterocyclic cores. This method allows a single-step synthesis of complex nitrogen heterocycles from easily available and cheap triazole precursors. In this Minireview, recent progress of the transition metal catalyzed denitrogenative transannulation of a triazole ring, which was discovered in 2007, is discussed. PMID:22121072

  12. 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

  13. Mechanism of the Orotidine 5?Monophosphate Decarboxylase-Catalyzed Reaction: Evidence for Substrate Destabilization

    Microsoft Academic Search

    Kui K. Chan; M Wood; Alexander A. Fedorov; Elena V. Fedorov; Heidi J. Imker; Tina L. Amyes; John P. Richard; Steven C. Almo; John A. Gerlt

    2009-01-01

    The reaction catalyzed by orotidine 5'-monophosphate decarboxylase (OMPDC) involves a stabilized anionic intermediate, although the structural basis for the rate acceleration (kcat\\/knon, 7.1 x 1016) and proficiency (kcat\\/KM)\\/knon, 4.8 x 1022 M-1 is uncertain. That the OMPDCs from Methanothermobacter thermautotrophicus (MtOMPDC) and Saccharomyces cerevisiae (ScOMPDC) catalyze the exchange of H6 of the UMP product with solvent deuterium allows an estimate

  14. Copper-Catalyzed Enantioselective Additions to Oxocarbenium Ions: Alkynylation of Isochroman Acetals

    PubMed Central

    Maity, Prantik; Srinivas, Harathi D.; Watson, Mary P.

    2011-01-01

    We have developed an enantioselective, copper(I)-catalyzed addition of terminal alkynes to racemic isochroman acetals. This method is one of the first transition metal-catalyzed approaches to enantioselective additions to prochiral oxocarbenium ions. In this reaction, TMSOTf is used to form the oxocarbenium ion in situ under conditions compatible with simultaneous formation of the chiral copper acetylide. By using a bis(oxazoline) ligand, good yields and enantioselectivities are observed for a variety of enantioenriched 1-alkynyl isochromans. PMID:21988178

  15. Heterogeneous catalyzed decomposition reactions of dichlorodifluoromethane in the presence of water on ?-alumina

    Microsoft Academic Search

    E. Kemnitz; A. Kohne; E. Lieske

    1997-01-01

    The heterogeneous catalyzed decomposition of CCl2F2 (CFC-12) in the presence of water was investigated, employing ?-alumina as catalyst. The catalyzed hydrolysis reaction yields very high conversion degrees of CFC-12 in the first reaction stage. For a period of about 3 h there is a remarkable lack of balance between the amount of liberated HF and HCl owing to the uptake

  16. Potassium acetate-catalyzed acetylation of wood: reaction rates at low temperatures

    Microsoft Academic Search

    Eiichi Obataya; Kazuya Minato

    2009-01-01

    Spruce wood blocks were acetylated in the presence of potassium acetate (KAc) at 20, 40, 60, 80 and 120°C. At 20°C, the weight\\u000a percent gain (WPG) due to the KAc-catalyzed acetylation reached 20% in 18 days, whereas that due to pyridine-catalyzed acetylation\\u000a did not exceed 8%. The hygroscopicity and dimensional stability of the KAc-acetylated wood were the same as those of

  17. Origins of large rate enhancements in the Nazarov cyclization catalyzed by supramolecular encapsulation.

    PubMed

    Hastings, Courtney J; Bergman, Robert G; Raymond, Kenneth N

    2014-04-01

    The self-assembled supramolecular host [Ga4L6](12-) (1; L=N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) catalyzes the Nazarov cyclization of 1,3-pentadienols with extremely high levels of efficiency. The catalyzed reaction proceeds at a rate over a million times faster than that of the background reaction, an increase comparable to those observed in some enzymatic systems. A detailed study was conducted to elucidate the reaction mechanism of both the catalyzed and uncatalyzed Nazarov cyclization of pentadienols. Kinetic analysis and (18)O-exchange experiments implicate a mechanism, in which encapsulation, protonation, and water loss from substrate are reversible, followed by irreversible electrocyclization. Although electrocyclization is rate determining in the uncatalyzed reaction, the barrier for water loss and for electrocyclization are nearly equal in the assembly-catalyzed reaction. Analysis of the energetics of the catalyzed and uncatalyzed reaction revealed that transition-state stabilization contributes significantly to the dramatically enhanced rate of the catalyzed reaction. PMID:24615703

  18. Xanthine oxidase-catalyzed crosslinking of cell membrane proteins.

    PubMed

    Girotti, A W; Thomas, J P; Jordan, J E

    1986-12-01

    Isolated erythrocyte membranes exposed to protease-free xanthine oxidase plus xanthine and ferric iron undergo lipid peroxidation and protein crosslinking (appearance of high molecular weight aggregates on sodium dodecyl sulfate (SDS) gel electrophoresis). Spectrin is more susceptible to crosslinking than the other polypeptides. Thiol-reducible bonds (disulfides) as well as nonreducible bonds are generated, the former type relatively rapidly (detected within 10-20 min) and the latter type more slowly (usually detected after 1 h). Reducible crosslinking is inhibited by catalase, but not by superoxide dismutase, desferrioxamine, butylated hydroxyltoluene, and mannitol; whereas nonreducible crosslinking, like free radical lipid peroxidation, is inhibited by all of these agents except mannitol. Zinc(II) also inhibits lipid peroxidation, but stimulates disulfide bond formation to the virtual exclusion of all other crosslinking. Our results indicate that disulfide formation is dependent on H2O2, but not O2- or iron. However, O2-, H2O2, and iron are all required for lipid peroxidation and nondisulfide crosslinking, suggesting the intermediacy of OH generated via the iron-catalyzed Haber-Weiss reaction. The possible role of malonaldehyde (MDA, a by-product of lipid peroxidation) in the latter type of crosslinking was examined. Solubilized samples of xanthine/xanthine oxidase-treated membranes showed a strong visible fluorescence (emission maximum 450 nm; excitation 390 nm). This resembled the fluorescence of membranes treated with authentic MDA, which forms conjugated imine linkages between amino groups. Fluorescence scanning of SDS gels from MDA-treated membranes showed a strong signal coincident with crosslinked proteins and also one in the low molecular weight, nonprotein region, suggestive of aminolipid conjugates. Similar scanning on xanthine/xanthine oxidase-reacted membranes indicated that all fluorescence is associated with the lipid fraction. Thus, nonreducible protein crosslinks in this system do not appear to be of the MDA-derived, Schiff base type. PMID:3800391

  19. Computational biotransformation profile of paracetamol catalyzed by cytochrome p450.

    PubMed

    Ji, Li; Schüürmann, Gerrit

    2015-04-20

    The P450-catalyzed biotransformation of the analgesic drug paracetamol (PAR) is a long-debated topic, involving different mechanistic hypotheses as well as experimental evidence for the metabolites N-acetyl-p-benzoquinone imine (NAPQI), p-benzoquinone, acetamide, and 3-hydroxy-PAR. During the catalytic cycle of P450, a high-valent iron(IV)-oxo species known as Compound I (Cpd I) is formed as the ultimate oxidant, featuring two energetically close-lying ground states in the doublet (low-spin) and quartet (high-spin) spin states, respectively. In order to clarify the catalytic mechanism, a computational chemistry analysis has been undertaken for both the high- and low-spin routes, employing density functional theory (DFT) including PCM (polarized continuum-solvation model) that yields an approximate simulation of the bulk polarization exerted through the protein. The results demonstrate that hydrogen abstraction transfer (HAT) by the P450 oxidant Cpd I (FeO) is kinetically strongly preferred over the alternative pathways of an oxygen addition reaction (OAR) or two consecutive single-electron transfers (SET). Moreover, only the respective high-spin route yields N-acetyl-p-semiquinone imine (NAPSQI) as an intermediate that is converted to the electrophile N-acetyl-p-benzoquinone imine (NAPQI). By contrast, 3-hydroxy-PAR, acetamide, and p-benzoquinone as electrophilic and redox-active agent are formed predominantly in the low-spin state through reactions that do not involve NAPSQI. Thus, all experimentally observed PAR metabolites are in accord with an initial HAT from the phenolic oxygen, and NAPSQI should indeed be the precursor of NAPQI, both of which are generated only via the high-spin pathway. PMID:25548954

  20. The mechanism for iron-catalyzed alkene isomerization in solution

    SciTech Connect

    Sawyer, Karma R.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Harris, Charles B.

    2008-05-27

    Here we report nano- through microsecond time-resolved IR experiments of iron-catalyzed alkene isomerization in room-temperature solution. We have monitored the photochemistry of a model system, Fe(CO){sub 4}({eta}{sup 2}-1-hexene), in neat 1-hexene solution. UV-photolysis of the starting material leads to the dissociation of a single CO to form Fe(CO){sub 3}({eta}{sup 2}-1-hexene), in a singlet spin state. This CO loss complex shows a dramatic selectivity to form an allyl hydride, HFe(CO){sub 3}({eta}{sup 3}-C{sub 6}H{sub 11}), via an internal C-H bond-cleavage reaction in 5-25 ns. We find no evidence for the coordination of an alkene molecule from the bath to the CO loss complex, but do observe coordination to the allyl hydride, indicating that it is the key intermediate in the isomerization mechanism. Coordination of the alkene ligand to the allyl hydride leads to the formation of the bis-alkene isomers, Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) and Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2}. Because of the thermodynamic stability of Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) over Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2} (ca. 12 kcal/mol), nearly 100% of the alkene population will be 2-alkene. The results presented herein provide the first direct evidence for this mechanism in solution and suggest modifications to the currently accepted mechanism.

  1. DNA hydrolytic cleavage catalyzed by synthetic multinuclear metallonucleases.

    PubMed

    Liu, Changlin; Wang, Li

    2009-01-14

    Much effort has been directed at understanding the roles of metal ions in catalyzing the hydrolysis of phosphodiester bonds of nucleic acids. Nucleases are metalloenzymes that have a wide variety of active site motifs and that contain a variety of different metal ions. This property has made it difficult to propose a simple mechanism for these enzymes. Therefore, design and synthesis of metal complexes, which can mediate phosphodiester bond cleavage via hydrolytic pathways, are of important significance in elucidation of the catalytic mechanisms for the natural nucleases and in development of the biomacromolecule-targeted drugs. Recent progress has extended to the design of synthetic multinuclear metallonucleases containing two or more Fe(III), Zn(II), Cu(II), Co(II/III), or Ln(III/IV) ions. The ligands in these complexes include natural and nonnatural organic molecules, i.e., mainly benzimidazolyl- and pyridyl-based organic molecules, azamacrocyclic and aminocarboxylic derivatives, and their conjugates to polypeptides or oligonucleotides. The purpose of this perspective is to highlight: (1) the differences in structure and composition between natural and synthetic multinuclear metallonucleases; (2) the design strategies of synthetic multinuclear metallonucleases; (3) the relationship between the structures and nucleolytic activities of synthetic multinuclear metallonucleases; and (4) the cooperativities between metal sites, and between metal sites and ligands in the courses of phospodiester linkage hydrolysis. A comparison illustrates unifying themes in the catalysis of phosphodiester linkage hydrolysis by natural and synthetic multinuclear metallonucleases. Indeed, there are features that converge about the chemistry that provides insight into how changes in metal ions and ligands of both natural and synthetic metallonucleases may lead to the same overall outcome of phosphodiester backbone cleavage. In addition, we will also discuss the solvation effect of synthetic multinuclear metallonucleases and the challenges that should be faced toward the development of synthetic multinuclear metallonucleases with DNA sequence or structure selectivity by applying the principles of coordination and enzymatic chemistry. PMID:19089001

  2. Removal of emerging pollutants by Ru/TiO2-catalyzed permanganate oxidation.

    PubMed

    Zhang, Jing; Sun, Bo; Xiong, Xinmei; Gao, Naiyun; Song, Weihua; Du, Erdeng; Guan, Xiaohong; Zhou, Gongming

    2014-10-15

    TiO2 supported ruthenium nanoparticles, Ru/TiO2 (0.94‰ as Ru), was synthesized to catalyze permanganate oxidation for degrading emerging pollutants (EPs) with diverse organic moieties. The presence of 1.0 g L(-1) Ru/TiO2 increased the second order reaction rate constants of bisphenol A, diclofenac, acetaminophen, sulfamethoxazole, benzotriazole, carbamazepine, butylparaben, diclofenac, ciprofloxacin and aniline at mg L(-1) level (5.0 ?M) by permanganate oxidation at pH 7.0 by 0.3-119 times. The second order reaction rate constants of EPs with permanganate or Ru/TiO2-catalyzed permanganate oxidation obtained at EPs concentration of mg L(-1) level (5.0 ?M) underestimated those obtained at EPs concentration of ?g L(-1) level (0.050 ?M). Ru/TiO2-catalyzed permanganate could decompose a mixture of nine EPs at ?g L(-1) level efficiently and the second order rate constant for each EP was not decreased due to the competition of other EPs. The toxicity tests revealed that Ru/TiO2-catalyzed permanganate oxidation was effective not only for elimination of EPs but also for detoxification. The removal rates of sulfamethoxazole by Ru/TiO2-catalyzed permanganate oxidation in ten successive cycles remained almost constant in ultrapure water and slightly decreased in Songhua river water since the sixth run, indicating the satisfactory stability of Ru/TiO2. Ru/TiO2-catalyzed permanganate oxidation was selective and could remove selected EPs spiked in real waters more efficiently than chlorination. Therefore, Ru/TiO2-catalyzed permanganate oxidation is promising for removing EPs with electron-rich moieties. PMID:25016299

  3. Cysteine oxidation reactions catalyzed by a mononuclear non-heme iron enzyme (OvoA) in ovothiol biosynthesis.

    PubMed

    Song, Heng; Her, Ampon Sae; Raso, Fiona; Zhen, Zhibin; Huo, Yuda; Liu, Pinghua

    2014-04-18

    OvoA in ovothiol biosynthesis is a mononuclear non-heme iron enzyme catalyzing the oxidative coupling between histidine and cysteine. It can also catalyze the oxidative coupling between hercynine and cysteine, yet with a different regio-selectivity. Due to the potential application of this reaction for industrial ergothioneine production, in this study, we systematically characterized OvoA by a combination of three different assays. Our studies revealed that OvoA can also catalyze the oxidation of cysteine to either cysteine sulfinic acid or cystine. Remarkably, these OvoA-catalyzed reactions can be systematically modulated by a slight modification of one of its substrates, histidine. PMID:24684381

  4. Copper-Catalyzed Intermolecular Amidation and Imidation of Unactivated Alkanes

    PubMed Central

    2015-01-01

    We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C–H bonds over tertiary C–H bonds and even occur at primary C–H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from ?-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C–H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C–H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product. PMID:24405209

  5. Cyclohexane oxidation catalyzed by titanium silicalite (TS-1): Overoxidation and comparison with other oxidation systems

    SciTech Connect

    Spinace, E.V.; Pastore, H.O.; Schuchardt, U. [Universidade Estadual de Campinas (Brazil)] [Universidade Estadual de Campinas (Brazil)

    1995-12-01

    At 1000{degrees}C cyclohexanone and cyclohexanone, obtained in the TS-1 catalyzed oxidation of cyclohexane, are further oxidized in uncatalyzed and TS-1 catalyzed reactions. Cyclohexanol is very selectively oxidized to cyclohexanone inside the porous system of TS-1 and unselectively oxidized to several oxidation products on the external surface. This unselective oxidation can be suppressed by the addition of 2,6-di-tert-butyl-4-methylphenol (BHT), which does not enter the molecular sieve pore system and which efficiently reduces uncatalyzed oxidation. Cyclohexanone oxidation is mostly uncatalyzed, forming pre-dominantly dicarboxylic acids, and is not influenced by BHT. The products of the TS-1 catalyzed cyclohexanone oxidation are partially retained in the porous system, thus explaining the deactivation of the catalyst. Comparison with other systems shows that the turnover frequency of the TS-1 catalyzed cyclohexane oxidation is very similar to that of the radical-chain process, thus suggesting that the rate-determining step of the TS-1 catalyzed reaction is also the homolytic cleavage of a C-H bond. 18 refs., 5 tabs.

  6. Metal-catalyzed cascade reactions: useful synthetic tools for the preparation of polycyclic arenes.

    PubMed

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

    2015-02-01

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

  7. Metabolism of Monoterpenes

    PubMed Central

    Croteau, Rodney; Hooper, Caroline Lee

    1978-01-01

    The essential oil from mature leaves of flowering peppermint (Mentha piperita L.) contains up to 15% (—)-menthyl acetate, and leaf discs converted exogenous (—)-[G-3H]menthol into this ester in approximately 15% yield of the incorporated precursor. Leaf extracts catalyzed the acetyl coenzyme A-dependent acetylation of (—)-[G-3H]menthol and the product of this transacetylase reaction was identified by radiochromatographic techniques. Transacetylase activity was located mainly in the 100,000g supernatant fraction, and the preparation was partially purified by combination of Sephadex G-100 gel filtration and chromatography on O-diethylaminoethyl-cellulose. The transacetylase had a molecular weight of about 37,000 as judged by Sephadex G-150 gel filtration, and a pH optimum near 9. The apparent Km and velocity for (—)-menthol were 0.3 mm and 16 nmol/hr· mg of protein, respectively. The saturation curve for acetyl coenzyme A was sigmoidal, showing apparent saturation near 0.1 mm. Dithioerythritol was required for maximum activity and stability of the enzyme, and the enzyme was inhibited by thiol directed reagents such as p-hydroxymercuribenzoate. Diisopropylfluorophosphate also inhibited transacylation suggesting the involvement of a serine residue in catalysis. The transacylase was highly specific for acetyl coenzyme A; propionyl coenzyme A and butyryl coenzyme A were not nearly as efficient as acyl donors (11% and 2%, respectively). However, the enzyme was much less selective with regard to the alcohol substrate, suggesting that the nature of the acetate ester synthesized in mint is more dependent on the type of alcohol available than on the specificity of the transacetylase. This is the first report on an enzyme involved in monoterpenol acetylation in plants. A very similar enzyme, catalyzing this key reaction in the metabolism of menthol, was also isolated from the flowers of peppermint. PMID:16660375

  8. Primary product of the horseradish peroxidase-catalyzed oxidation of pentachlorophenol

    SciTech Connect

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

    1999-05-01

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

  9. 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.

  10. [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

  11. Rhodium-Catalyzed Acyloxy Migration of Propargylic Esters in Cycloadditions, Inspiration from Recent “Gold Rush”

    PubMed Central

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

    2012-01-01

    Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most ?-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative addition, migratory insertion, and reductive elimination may lead to ample new opportunities for the design of new reactions. This tutorial review summarizes recent developments in Rh-catalyzed 1,3- and 1,2-acyloxy migration of propargylic esters in a number of cycloaddition reactions. Related Au- and Pt-catalyzed cycloadditions involving acyloxy migration are also discussed. PMID:22895533

  12. Pseudoglycosyltransferase Catalyzes Non-Glycosidic C-N Coupling in Validamycin A Biosynthesis

    PubMed Central

    Asamizu, Shumpei; Yang, Jongtae; Almabruk, Khaled H.; Mahmud, Taifo

    2011-01-01

    Glycosyltransferases are ubiquitous in nature. They catalyze a glycosidic bond formation between sugar donors and sugar or non-sugar acceptors to produce oligo/polysaccharides, glycoproteins, glycolipids, glycosylated natural products, and other sugar-containing entities. However, a trehalose 6-phosphate synthase-like protein has been found to catalyze an unprecedented non-glycosidic C-N bond formation in the biosynthesis of the aminocyclitol antibiotic validamycin A. This dedicated ‘pseudoglycosyltransferase’ catalyzes a condensation between GDP-valienol and validamine 7-phosphate to give validoxylamine A 7?-phosphate with net retention of the ‘anomeric’ configuration of the donor cyclitol in the product. The enzyme operates in sequence with a phosphatase, which dephosphorylates validoxylamine A 7?-phosphate to validoxylamine A. PMID:21766819

  13. 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.

  14. Arsenic effects and behavior in association with the Fe(II)-catalyzed transformation of schwertmannite.

    PubMed

    Burton, Edward D; Johnston, Scott G; Watling, Kym; Bush, Richard T; Keene, Annabelle F; Sullivan, Leigh A

    2010-03-15

    In acid-mine drainage and acid-sulfate soil environments, the cycling of Fe and As are often linked to the formation and fate of schwertmannite (Fe(8)O(8)(OH)(8-2x)(SO(4))(x)). When schwertmannite-rich material is subjected to near-neutral Fe(III)-reducing conditions (e.g., in reflooded acid-sulfate soils or mining-lake sediments), the resulting Fe(II) can catalyze transformation of schwertmannite to goethite. This work examines the effects of arsenic(V) and arsenic(III) on the Fe(II)-catalyzed transformation of schwertmannite and investigates the associated consequences of this mineral transformation for arsenic mobilization. A series of 9-day anoxic transformation experiments were conducted with synthetic schwertmannite and various additions of Fe(II), As(III), and As(V). X-ray diffraction (XRD) and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy demonstrated that, in the absence of Fe(II), schwertmannite persisted as the dominant mineral phase. Under arsenic-free conditions, 10 mM Fe(II) catalyzed rapid and complete transformation of schwertmannite to goethite. However, the magnitude of Fe(II)-catalyzed transformation decreased to 72% in the presence of 1 mM As(III) and to only 6% in the presence of 1 mM As(V). This partial Fe(II)-catalyzed transformation of As(III)-sorbed schwertmannite did not cause considerable As(III) desorption. In contrast, the formation of goethite via partial transformation of As(III)- and As(V)-sorbed schwertmannite significantly decreased arsenic mobilization under Fe(III)-reducing conditions. This implies that the Fe(II)-catalyzed transformation of schwertmannite to goethite may help to stabilize solid-phase arsenic and retard its subsequent release to groundwater. PMID:20148551

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

    E-print Network

    Roy Choudhury, Rita

    1984-01-01

    THE pH DEPENDENCE (P DIHYDROGRCTIC ACID SYNTHESIS CATALYZED BY ZINC AND COBALT DIHYDROORC1IASE A Thesis by RITA ROY CHOUDHJRY ~roved style and content: ( zrrren af Ccmittee) (Manter ) ( ) ( of Iepsrt~t) Ann~st I984 The pH Dependence... 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...

  16. 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

  17. An alternative approach to aldol reactions: gold-catalyzed formation of boron enolates from alkynes.

    PubMed

    Körner, Cindy; Starkov, Pavel; Sheppard, Tom D

    2010-05-01

    A new method for enolate generation via the gold-catalyzed addition of boronic acids to alkynes is reported. The formation of boron enolates from readily accessible ortho-alkynylbenzeneboronic acids proceeds rapidly with 2 mol % PPh(3)AuNTf(2) at ambient temperature. The enolates undergo aldol reaction with an aldehyde present in the reaction mixture to give cyclic boronate esters, which can be subsequently transformed into phenols, biaryls, or dihydrobenzofurans via oxidation, Suzuki-Miyaura, or intramolecular Chan-Lam coupling, respectively. A combined gold/boronic acid catalyzed aldol condensation reaction of an alkynyl aldehyde was also successfully achieved. PMID:20380452

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  19. Tandem three-component reactions of aldehyde, alkyl acrylate, and dialkylmalonate catalyzed by ethyl diphenylphosphine.

    PubMed

    Jang, Yeong-Jiunn; Syu, Siang-En; Jhang, Yi-Wun; Lee, Yu-Ting; Lee, Chia-Jui; Chen, Ko-Wei; Das, Utpal; Lin, Wenwei

    2012-01-01

    A new highly efficient three-component reaction of alkyl acrylate, aldehyde and dialkyl malonate using ethyl diphenylphosphine as organocatalyst has been described. Various highly functional compounds bearing hydroxyl groups and the ester functions can be easily prepared in moderate to good yields according to our one-step procedure. The reactions are believed to proceed via Morita-Baylis-Hillman reactions of alkyl acrylate and aldehydes, followed by the Michael addition reactions of dialkyl malonates. Our reactions indicated that the intermediate species formed in the phosphine-catalyzed MBH reaction are an effective organic base to catalyze the Michael addition reactions of dialkyl malonates to the preformed MBH adducts. PMID:22446986

  20. Copper-catalyzed trifluoromethylthiolation of aryl halides with diverse directing groups.

    PubMed

    Xu, Jiabin; Mu, Xin; Chen, Pinhong; Ye, Jinxing; Liu, Guosheng

    2014-08-01

    The expansion of cross-coupling components in Cu-catalyzed C-X bond forming reactions have received much attention recently. A novel Cu-catalyzed trifluoromethylthiolation of aryl bromides and iodides with the assistance of versatile directing groups such as pyridyl, methyl ester, amide, imine and oxime was reported. CuBr was used as the catalyst, and 1,10-phenanthroline as the ligand. By changing the solvent from acetonitrile to DMF, the coupling process could even take place at room temperature. PMID:25036156

  1. Threonine Synthetase-Catalyzed Conversion of Phosphohomoserine to ?-Ketobutyrate in Bacillus subtilis

    PubMed Central

    Schildkraut, Ira; Greer, Sheldon

    1973-01-01

    An enzyme activity of Bacillus subtilis has been found that catalyzes the dephosphorylation and deamination of phosphohomoserine to ?-ketobutyrate, resulting in a bypass of threonine in isoleucine biosynthesis. In crude extracts of a strain deficient in the biosynthetic isoleucine-inhibitable threonine dehydratase, phosphohomoserine was converted to ?-ketobutyrate. Phosphohomoserine conversion to ?-ketobutyrate was shown not to involve a threonine intermediate. Single mutational events affecting threonine synthetase also affected the phosphohomoserine-deaminating activity, suggesting that the deamination of phosphohomoserine was catalyzed by the threonine synthetase enzyme. It was demonstrated in vivo, in a strain deficient in the biosynthetic threonine dehydratase, that isoleucine was synthesized from homoserine without intermediate formation of threonine. PMID:4199513

  2. Ni(ii)/BINOL-catalyzed alkenylation of unactivated C(sp(3))-H bonds.

    PubMed

    Liu, Yue-Jin; Zhang, Zhuo-Zhuo; Yan, Sheng-Yi; Liu, Yan-Hua; Shi, Bing-Feng

    2015-04-23

    The first nickel-catalyzed alkenylation of unactivated C(sp(3))-H bonds with vinyl iodides is described. The catalytic system comprises an inexpensive and air-stable Ni(acac)2 as the catalyst and BINOL as the ligand, which is highly efficient for the alkenylation of ?-methyl C(sp(3))-H bonds of a broad range of aliphatic carboxamides. The resulting olefins can serve as versatile handles for further preparation. Additionally, we also demonstrated the synthesis of functionalized carboxamides bearing ?-quaternary carbon centers from simple pivalamide via nickel-catalyzed sequential C(sp(3))-H bond functionalization. PMID:25857332

  3. Silica, Alumina and Clay Catalyzed Peptide Bond Formation: Enhanced Efficiency of Alumina Catalyst

    NASA Astrophysics Data System (ADS)

    Bujdák, Juraj; Rode, Bernd M.

    1999-10-01

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

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

    PubMed

    Bujdák, J; Rode, B M

    1999-10-01

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

  5. P,N,N-pincer nickel-catalyzed cross-coupling of aryl fluorides and chlorides.

    PubMed

    Wu, Dan; Wang, Zhong-Xia

    2014-09-01

    P,N,N-Pincer nickel complexes [Ni(Cl){N(2-R2PC6H4)(2'-Me2NC6H4)}] (R = Ph, 3a; R = Pr(i), 3b; R = Cy, 3c) were synthesized and their catalysis toward the Kumada or Negishi cross-coupling reaction of aryl fluorides and chlorides was evaluated. Complex 3a effectively catalyzes the cross-coupling of (hetero)aryl fluorides with aryl Grignard reagents at room temperature. Complex 3a also catalyzes the cross-coupling of (hetero)aryl chlorides and arylzinc reagents at 80 °C with low catalyst loadings and good functional group compatibility. PMID:25012049

  6. Nickel-Catalyzed Amination of Aryl Chlorides and Sulfamates in 2-Methyl-THF.

    PubMed

    Fine Nathel, Noah F; Kim, Junyong; Hie, Liana; Jiang, Xingyu; Garg, Neil K

    2014-09-01

    The nickel-catalyzed amination of aryl O-sulfamates and chlorides using the green solvent 2-methyl-THF is reported. This methodology employs the commercially available and air-stable precatalyst NiCl2(DME), is broad in scope, and provides access to aryl amines in synthetically useful yields. The utility of this methodology is underscored by examples of gram-scale couplings conducted with catalyst loadings as low as 1 mol % nickel. Moreover, the nickel-catalyzed amination described is tolerant of heterocycles and should prove useful in the synthesis of pharmaceutical candidates and other heteroatom-containing compounds. PMID:25243095

  7. Acid-catalyzed plasmenylcholine hydrolysis and its effect on bilayer permeability: a quantitative study

    Microsoft Academic Search

    Oleg V. Gerasimov; Annette Schwan; David H. Thompson

    1997-01-01

    This laboratory has previously shown (Anderson, V.C. and Thompson, D.H. (1992) Biochim. Biophys. Acta 1109, 33–42; Thompson, D.H., Gerasimov, O.V., Wheeler, J.J., Rui, Y. and Anderson, V.C. (1996) Biochim. Biophys. Acta 1279, 25–34), that plasmenylcholine (1-alk-1?-enyl-2-palmitoyl-sn-glycero-3-phosphocholine; PlsPamCho) liposomes release hydrophilic contents upon photooxidation or acid-catalyzed hydrolysis. We now report the kinetics and chemical mechanism of the acid-catalyzed reaction and its

  8. Mild palladium-catalyzed cyanation of (hetero)aryl halides and triflates in aqueous media.

    PubMed

    Cohen, Daniel T; Buchwald, Stephen L

    2015-01-16

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

  9. The mechanisms of S-nitrosothiol decomposition catalyzed by iron.

    PubMed

    Vanin, Anatoly F; Papina, Alina A; Serezhenkov, Vladimir A; Koppenol, Willem H

    2004-03-01

    The mechanisms of S-nitrosothiol transformation into paramagnetic dinitrosyl iron complexes (DNICs) with thiol- or non-thiol ligands or mononitrosyl iron complex (MNICs) with N-methyl-D-glucamine dithiocarbamate catalyzed by iron(II) ions under anaerobic conditions were studied by monitoring EPR or optical features of the complexes and S-nitrosothiols. The kinetic investigations demonstrated the appearance of short-living paramagnetic mononitrosyl-iron complex with L-cysteine prior to the formation of stable dinitrosyl-iron complex with cysteine in the solution of iron(II)-citrate complex (50-100 microM), S-nitrosocysteine (400 microM), and L-cysteine (20 mM) in 100 mM Hepes buffer (pH 7.4). The addition of deoxyhemoglobin (100 microM) did not influence the process, which points to a direct interaction between S-nitrosocysteine and iron(II) ions to yield DNIC. The reaction of DNIC-cysteine formation is first- and second-order in iron and S-nitrosocysteine, respectively. The third-order rate constant is (1.0 +/- 0.2) x 10(5) M(-2) s(-1) (estimated from EPR results) or (2.0 +/- 0.1) x 10(4) M(-2) s(-1) (estimated by optical method). A similar process of DNIC-cysteine formation was observed in a solution of iron(II)-citrate complex, L-cysteine, and NO-proline (200 microM) as a NO* donor. The appearance of a less stable dinitrosyl-iron complex with phosphate was detected when solutions of iron(II)-citrate containing 100 mM phosphate buffer (pH 7.4) were mixed with S-nitrosocysteine or NO-proline. The rapid formation of DNIC with phosphate was followed by its decay. When the concentration of L-cysteine in solutions was reduced from 20 to 1 mM, the life-time of the DNIC-cysteine diminished notably; this was caused by consumption of L-cysteine in the process of DNIC-cysteine formation from S-nitrosocysteine and iron. Thus, L-cysteine is consumed. Formation of DNIC with glutathione was also observed in a solution of glutathione (20 mM), S-nitrosoglutathione (400 microM), and iron(II) complex (800 microM) in 100 mM Hepes buffer (pH 7.4), but the rate of formation was about 10 times slower than the formation of the DNIC-cysteine. The rate of MNIC-MGD formation from iron(II)-MGD complexes and S-nitrosocysteine was first-order in both reactants. The second-order rate constant for this reaction, estimated from EPR measurements, was 30 +/- 5 M(-1) s(-1). Rate constants of MNIC-MGD formation from iron(II)-MGD and the more stable S-nitrosoglutathione and S-nitroso-D,L-penicillamine were equal to 3.0 +/- 0.3 and 0.3 +/- 0.05 M(-1) s(-1), respectively. Thus, the concerted mechanism of DNIC and MNIC formation from S-nitrosothiols and iron(II) ions can be suggested to be predominant. PMID:15135359

  10. Iron(III) catalyzed direct synthesis of cis-2,7-disubstituted oxepanes. The shortest total synthesis of (+)-isolaurepan.

    PubMed

    Purino, Martín A; Ramírez, Miguel A; Daranas, Antonio H; Martín, Víctor S; Padrón, Juan I

    2012-12-01

    Prins cyclization of bis-homoallylic alcohols with aldehydes catalyzed by iron(III) salts shows excellent cis selectivity and yields to form 2,7-disubstituted oxepanes. The iron(III) is able to catalyze this process with unactivated olefins. This cyclization was used as the key step in the shortest total synthesis of (+)-isolaurepan. PMID:23167915

  11. Accelerating Effect of Umbelliferone on Peroxidase-Catalyzed Oxidation of Indole-3-acetic Acid at Neutral pH

    E-print Network

    Krylov, Sergey

    Accelerating Effect of Umbelliferone on Peroxidase-Catalyzed Oxidation of Indole-3-acetic Acid The acceleration by the phenol umbelliferone (7-hydroxycoumarin) of the horseradish peroxidase (HRP) catalyzed no further effect. The rate constants for the peroxidase compounds I and II (HRP-I and HRP-II) reductions

  12. Rhodium-catalyzed 1,3-acyloxy migration and subsequent intramolecular [4 + 2] cycloaddition of vinylallene and unactivated alkyne†

    PubMed Central

    Huang, Suyu; Li, Xiaoxun; Lin, Claire L.; Guzei, Ilia A.

    2012-01-01

    A Rh-catalyzed 1,3-acyloxy migration of propargyl ester followed by intramolecular [4 + 2] cycloaddition of vinylallene and unactivated alkyne was developed. This tandem reaction provides access to bicyclic compounds containing a highly functionalized isotoluene or cyclohexenone structural motif, while only aromatic compounds were observed in related transition metal-catalyzed cycloadditions. PMID:22252254

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

    E-print Network

    Toste, Dean

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

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

    E-print Network

    Toste, Dean

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

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

    E-print Network

    He, Chuan

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

  16. 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

  17. 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 ...

  18. Rhodium-catalyzed dehydrogenative coupling of phenylheteroarenes with alkynes or alkenes.

    PubMed

    Iitsuka, Tomonori; Hirano, Koji; Satoh, Tetsuya; Miura, Masahiro

    2015-03-01

    Benzo-fused tri- to heptacyclic heteroarenes were effectively constructed by the rhodium-catalyzed dehydrogenative coupling of phenylheteroarenes with alkynes. Using alkenes as coupling partners, dehydrogenative alkenylation took place selectively on the phenyl moiety of phenylheteroarenes. Several experiments with deuterium-labeled substrates indicated that double C-H bond cleavages take place even in the reaction with alkenes. PMID:25686408

  19. Rhodium-catalyzed cyclopropanation of fluorinated olefins: a straightforward route to highly functionalized fluorocyclopropanes.

    PubMed

    Pons, Amandine; Beucher, Hélène; Ivashkin, Pavel; Lemonnier, Gérald; Poisson, Thomas; Charette, André B; Jubault, Philippe; Pannecoucke, Xavier

    2015-04-01

    An efficient access to highly functionalized monofluorocyclopropanes is described. The developed methodology allowed straightforward access to a large panel of polysubstituted fluorinated cyclopropanes in good to excellent yields and good diastereoselectivities. The Rh-catalyzed cyclopropanation proved to be efficient on several fluorinated olefins and several diazo compounds. This method represents the first general route to complex fluorinated cyclopropanes. PMID:25768041

  20. Rhodium(III)-catalyzed vinylic C-H activation: a direct route toward pyridinium salts.

    PubMed

    Luo, Ching-Zong; Jayakumar, Jayachandran; Gandeepan, Parthasarathy; Wu, Yun-Ching; Cheng, Chien-Hong

    2015-02-20

    A synthetic method for highly substituted pyridinium salts from the multicomponent reaction of vinyl ketones/aldehydes, amines, and alkynes using a rhodium catalyst is demonstrated. The catalytic reaction proceeds via an in situ generated imine-assisted Rh(III)-catalyzed vinylic C-H activation. PMID:25642795

  1. Chiral pyrrolidines and piperidines from enantioselective rhodium-catalyzed cascade arylative cyclization.

    PubMed

    Serpier, Fabien; Flamme, Benjamin; Brayer, Jean-Louis; Folléas, Benoît; Darses, Sylvain

    2015-04-01

    A new rhodium-catalyzed asymmetric arylative cyclization of nitrogen-tethered alkyne-enoate with arylboronic acids is described. In this process two new carbon-carbon bonds and one stereocenter are formed, providing access to pyrrolidines and piperidines with good enantioselectivities by to the use of C1-symmetric chiral monosubstituted diene ligands. PMID:25763595

  2. Rhodium-catalyzed hydroarylation of alkynes via tetrazole-directed C-H activation.

    PubMed

    Chen, Bin; Jiang, Yan; Cheng, Jiang; Yu, Jin-Tao

    2015-03-14

    A rhodium-catalyzed hydroarylation of alkynes with aryl tetrazoles through tetrazole-directed C-H activation was developed. This procedure has broad substrate scopes, and a variety of mono- and dialkenylated products were regioselectively obtained in moderate to excellent yields. PMID:25651394

  3. Rhodium-Catalyzed Activation and Functionalization of the C-C Bond of Biphenylene

    E-print Network

    Jones, William D.

    Rhodium-Catalyzed Activation and Functionalization of the C-C Bond of Biphenylene Carl N. Iverson August 29, 2001 Biphenylene reacts with the rhodium(I) dimer [(dtbpm)RhCl]2 (1) (dtbpm ) bis have been stoichiometric, although catalytic reactions are known.2 Rhodium complexes in particular have

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

    PubMed Central

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

    2014-01-01

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

  5. 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, and Mario J. Molina (see pages 9422­9427) CHEMISTRY Fusing silk and silica An engineered protein combining the flexibility and tensile strength of spider silk with the resilience of silica has been developed. The result

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

    EPA Science Inventory

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

  7. Polymer-Supported Siloxane Transfer Agents for Pd-Catalyzed Cross-Coupling Reactions

    PubMed Central

    Nguyen, Minh H.; Smith, Amos B.

    2013-01-01

    The design, synthesis and validation of a ROMP polymer supporting siloxane transfer agents have been achieved that permit efficient palladium-catalyzed cross-coupling reactions. The solubility properties of the polymer not only facilitate product purification, but also recycling without significant loss of cross-coupling activity. PMID:23901881

  8. Electron Transfer Catalyzed [2 + 2] Cycloreversion of Benzene G. Devi Reddy and Olaf Wiest*

    E-print Network

    Hudlicky, Tomas

    Electron Transfer Catalyzed [2 + 2] Cycloreversion of Benzene Dimers G. Devi Reddy and Olaf Wiest, Florida 32611-7200 Received December 8, 1998 The catalysis of the [2 + 2] cycloreversion of the anti-o,o-benzene dimer 1 and the syn-o,o- naphthalene-benzene dimer 2 through thermal and photoinduced electron transfer

  9. Ytterbium triflate hydrate catalyzed Michael addition and cyclocondensation of ?,?-unsaturated ketones with active methylene compounds

    Microsoft Academic Search

    Zhi Wei Chen; Yan Li Wang; Ren Er Chen; Wei Ke Su

    2008-01-01

    Catalyzed by ytterbium(III) triflate hydrate [Yb(OTf)3·xH2O], the Michael addition and cyclocondensation of ?,?-unsaturated ketones with active methylene compounds to afford the 1,4-adducts and benzo[b]pyran derivatives, respectively were studied.

  10. Palladium-catalyzed regio-selective oxidative C-H bond acylation of azoxybenzenes with alcohols.

    PubMed

    Hou, Lekai; Chen, Xiangxiang; Li, Shuang; Cai, Suxian; Zhao, Yanxia; Sun, Meng; Yang, Xiao-Juan

    2015-04-14

    A palladium-catalyzed regio-selective acylation of C-H bonds of azoxybenzenes with alcohols was developed using tert-butyl hydroperoxide (TBHP) as an oxidant. Alcohol derivatives can act as effective acyl precursors in situ, which are less toxic, inexpensive, stable, and commercially available. These transformations proceeded smoothly and could tolerate a variety of functional groups. PMID:25723965

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

    E-print Network

    Vallino, Joseph J.

    from yeast cells the enzymes catalyzing alcoholic fermentation. This achievement clearly demonstrated of biochemistry is the history of en- zyme research. The name enzyme ("in yeast") was not used until 1877, but much earlier it was suspected that biological catalysts are involved in the fermentation of sugar

  12. High fidelity of RecA-catalyzed recombination: a watchdog of genetic diversity

    E-print Network

    Tlusty, Tsvi

    High fidelity of RecA-catalyzed recombination: a watchdog of genetic diversity Dror Sagi, Tsvi recombination plays a key role in generating genetic diversity, while maintaining protein functionality of heterology was studied in vitro, using fluores- cence resonant energy transfer. RecA can detect single

  13. Ni-Catalyzed direct 1,4-difunctionalization of [60]fullerene with benzyl bromides.

    PubMed

    Si, Weili; Zhang, Xuan; Asao, Naoki; Yamamoto, Yoshinori; Jin, Tienan

    2015-03-26

    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. Palladium-Catalyzed Intermolecular Aminocarbonylation of Alkenes: Efficient Access of ?-Amino Acid Derivatives.

    PubMed

    Cheng, Jiashun; Qi, Xiaoxu; Li, Ming; Chen, Pinhong; Liu, Guosheng

    2015-02-25

    A novel palladium-catalyzed intermolecular aminocarbonylation of alkenes has been developed in which the employment of hypervalent iodine reagent can accelerate the intermolecular aminopalladation, which thus provides the successful catalytic transformation. The current transformation presents one of the most convenient methods to generate ?-amino acid derivatives from simple alkenes. PMID:25676745

  15. Pd-Catalyzed CdC Double-Bond Formation by Coupling of

    E-print Network

    Wang, Jianbo

    Pd-Catalyzed CdC Double-Bond Formation by Coupling of N-Tosylhydrazones with Benzyl Halides Qing-tosylhydrazones with benzyl halides affords di- and trisubstituted olefins in high yields with excellent stereoselectivity-bond formation is one of the most fundamental transformations in synthetic organic chemistry. Among the various

  16. Modification of vegetable oils. VII. Alkali catalyzed interesterification of peanut oil with ethanol

    Microsoft Academic Search

    R. O. Feuge; Audrey T. Gros

    1949-01-01

    HE alkali-catalyzed displacement of the glycerol in a fat by methanol or ethanol is an important reaction in fat and oil technology. Besides producing monoesters for use as such, the reaction simplifies the manufacture of some soaps, especially anhydrous soaps (2, 3); and it is valuable in conjunction with processes for fraetionating fatty acids. Potentially the reaction is important in

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

    PubMed Central

    Takebayashi, Satoshi; Shizuno, Tsubasa; Otani, Takashi

    2012-01-01

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

  18. Stereoselective Rhodium-Catalyzed [3 + 2 + 1] Carbocyclization of Alkenylidenecyclopropanes with Carbon Monoxide: Theoretical

    E-print Network

    Baik, Mu-Hyun

    the synthetic utility of this transformation. The design and implementation of new metal-catalyzed higher of the factors that control the selectivity. We3 and others4 have demonstrated the importance of theoretical-fused bicyclohexenones 3 in a highly efficient and stereoselective manner (Scheme 1).6 Devising a reliable computer model

  19. EVALUATION OF THE FULL-SCALE BASE CATALYZED DECOMPOSITION PROCESS (BCDP) UNIT LOCATED IN GUAM

    EPA Science Inventory

    This report summarizes performance data collected in February 1997 on the removal of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) from soil fed to a first-stage rotary kiln reactor of the Base Catalyzed Dec...

  20. Laccase-catalyzed oxidation of bisphenol A with the aid of additives

    Microsoft Academic Search

    Young-Jin Kim; James A. Nicell

    2006-01-01

    Laccase catalyzes the oxidation and polymerization of aromatic compounds in the presence of molecular oxygen. Four soluble compounds were evaluated as additives to maintain enzyme stability and enhance substrate conversion for environmental applications: namely, polyvinyl alcohol, Ficoll, polyethylene glycol (PEG), and alkyl betaine. All additives enhanced the transformation of bisphenol A (BPA) to similar degrees when present in sufficient amounts,

  1. N-Nosyl Oxaziridines as Terminal Oxidants in Copper(II)-Catalyzed Olefin Oxyaminations

    PubMed Central

    DePorter, Sandra M.; Jacobsen, Ashley C.; Partridge, Katherine M.; Williamson, Kevin S.; Yoon, Tehshik P.

    2010-01-01

    We report that N-4-nosyl-3-phenyloxaziridine is an effective terminal oxidant for copper(II)-catalyzed oxyamination recently developed in our labs. This oxaziridine can be prepared on multi-gram scale and is easily purified by recrystallization. The products of oxyamination using this oxaziridine bear protecting groups that can be readily removed in high yields under mild conditions. PMID:21076655

  2. N-Nosyl Oxaziridines as Terminal Oxidants in Copper(II)-Catalyzed Olefin Oxyaminations.

    PubMed

    Deporter, Sandra M; Jacobsen, Ashley C; Partridge, Katherine M; Williamson, Kevin S; Yoon, Tehshik P

    2010-10-01

    We report that N-4-nosyl-3-phenyloxaziridine is an effective terminal oxidant for copper(II)-catalyzed oxyamination recently developed in our labs. This oxaziridine can be prepared on multi-gram scale and is easily purified by recrystallization. The products of oxyamination using this oxaziridine bear protecting groups that can be readily removed in high yields under mild conditions. PMID:21076655

  3. The Roles of Ordinary and Soret Diffusion in the Metal-Catalyzed Formation of Filamentous Carbon

    Microsoft Academic Search

    W. L. Holstein

    1995-01-01

    The rate-determining step for the metal-catalyzed formation of filamentous carbon from hydrocarbons and carbon monoxide is commonly assumed to be diffusion of dissolved carbon through the metal particle. The driving force for the diffusion process has been proposed to be either an isothermal carbon concentration gradient or a temperature gradient, the latter leading to Soret diffusion (mass transfer due to

  4. 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

  5. USE OF CRITICAL CARBON DIOXIDE TO OPTIMIZE AN ENZYME CATALYZED REACTION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It was hypothesized that the equilibrium point of an enzyme-catalyzed reaction could be shifted to the right if the product could be partitioned into an immiscible carbon dioxide (CO2) phase. The molar ratios of starting material to product in CO2 were compared over a range of temperatures and pres...

  6. Novel Intermolecular Iterative Mechanism for Biosynthesis of Mycoketide Catalyzed by a Bimodular Polyketide Synthase

    Microsoft Academic Search

    Tarun Chopra; Srijita Banerjee; Sarika Gupta; Gitanjali Yadav; Swadha Anand; Avadhesha Surolia; Rajendra P Roy; Debasisa Mohanty; Rajesh S Gokhale

    2008-01-01

    In recent years, remarkable versatility of polyketide synthases (PKSs) has been recognized; both in terms of their structural and functional organization as well as their ability to produce compounds other than typical secondary metabolites. Multifunctional Type I PKSs catalyze the biosynthesis of polyketide products by either using the same active sites repetitively (iterative) or by using these catalytic domains only

  7. Synthesis of oxazocenones via gold(I)-catalyzed 8-endo-dig hydroalkoxylation of alkynamides.

    PubMed

    Scully, Stephen S; Zheng, Shao-Liang; Wagner, Bridget K; Schreiber, Stuart L

    2015-02-01

    Several benzoxazocenones have been found to exhibit novel cellular activities. In the present study, we report a gold(I)-catalyzed 8-endo-dig hydroalkoxylation reaction of alkynamides to access analogous oxazocenone scaffolds. This methodology provided an advanced intermediate, which was elaborated to a des-benzo analog of a bioactive benzoxazocenone. PMID:25569027

  8. 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.

  9. Advances in palladium-catalyzed carbon-nitrogen bond forming processes

    E-print Network

    Tundel, Rachel E. (Rachel Elizabeth)

    2006-01-01

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

  10. Catalyzed ring-opening polymerization of epoxidized soybean oil by hydrated and anhydrous fluoroantimonic acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by the super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), and the anhydrous form (HSbF6) in ethyl acetate was conducted in an effort to develop useful biodegradable polymers. The resulting polymerized ESO (SA-RPESO and SAA-...

  11. Synthesis of 2,4-diarylsubstituted-pyridines through a Ru-catalyzed four component reaction.

    PubMed

    Bai, Yang; Tang, Lichang; Huang, Huawen; Deng, Guo-Jun

    2015-03-31

    A ruthenium-catalyzed one-pot synthesis of 2,4-diarylsubstituted pyridines from acetophenones, ammonium acetate and DMF under an oxygen atmosphere is described. The carbon atom situated at C6 of the pyridine ring comes from the methyl group of DMF and the nitrogen atom comes from ammonium acetate. PMID:25764281

  12. Clickable 5'-?-Ferrocenyl Adenosine Triphosphate Bioconjugates in Kinase-Catalyzed Phosphorylations.

    PubMed

    Wang, Nan; She, Zhe; Lin, Yen-Chun; Marti?, Sanela; Mann, David J; Kraatz, Heinz-Bernhard

    2015-03-23

    Clickable co-substrate: A tri-functional 5'-?-ferrocenyl adenosine triphosphate (Fc-ATP) derivative containing a clickable site was synthesized. This compound is an effective co-substrate in kinase-catalyzed phosphorylation reactions, which can be detected by both electrochemical and immunoassay detection methods. The clickable reaction site makes direct modification possible, which greatly expands its application. PMID:25676877

  13. Palladium-catalyzed insertion of ?,?-unsaturated N-tosylhydrazones and trapping with carbon nucleophiles.

    PubMed

    Ye, Yu-Ying; Zhou, Ping-Xin; Luo, Jian-Yi; Zhong, Mei-Jin; Liang, Yong-Min

    2013-10-01

    Palladium-catalyzed carbene migratory insertion-cyclization reactions were reported, delivering dihydronaphthalene and indene derivatives in moderate to good yields. A three-component cross-coupling was also developed. The reactions are easy to handle, under mild conditions and various functional groups are tolerated. PMID:24056675

  14. Highly Stereoselective Ruthenium(II)-Catalyzed Direct C2-syn-Alkenylation of Indoles with Alkynes.

    PubMed

    Zhang, Wei; Wei, Jun; Fu, Shaomin; Lin, Dongen; Jiang, Huanfeng; Zeng, Wei

    2015-03-20

    A carboamide-directed ruthenium-catalyzed C2-hydroindolation of alkynes has been described. This transformation provides a rapid access to free (N-H) C2-syn-alkenylated indole derivatives with the assistance of copper(II) salts, in which the directing group is removed via a one-pot process. PMID:25746416

  15. Synthesis of aryldiazoacetates through palladium(0)-catalyzed deacylative cross-coupling of aryl iodides with acyldiazoacetates.

    PubMed

    Ye, Fei; Wang, Chengpeng; Zhang, Yan; Wang, Jianbo

    2014-10-20

    Palladium(0)-catalyzed deacylative cross-coupling of aryl iodides and acyldiazocarbonyl compounds can be achieved at room temperature under mild reaction conditions. The coupling reaction represents a highly efficient and general method for the synthesis of aryldiazocarbonyl compounds, which have found wide and increasing applications as precursors for generating donor/acceptor-substituted metallocarbenes. PMID:25196584

  16. Iodine-catalyzed allylic alkylation of sulfonamides and carbamates with allylic alcohols at room temperature

    Microsoft Academic Search

    Wenhan Wu; Weidong Rao; Ya Qin Er; Joanna Kejun Loh; Chai Yun Poh; Philip Wai Hong Chan

    2008-01-01

    A highly efficient iodine-catalyzed allylic alkylation of a wide variety of sulfonamides and carbamates with allylic alcohols is reported herein. The reaction is operationally straightforward and proceeds under very mild conditions at room temperature in good to excellent yields (up to 99%).

  17. Iodine-catalyzed allylation of 1,3-dicarbonyl compounds with allylic alcohols at room temperature

    Microsoft Academic Search

    Weidong Rao; Adeline Hui Ling Tay; Pei Jing Goh; Jessica Mun Ling Choy; Justin Kaijie Ke; Philip Wai Hong Chan

    2008-01-01

    A highly efficient iodine-catalyzed allylation of 1,3-dicarbonyl compounds with a wide variety of allylic alcohols has been developed. The reaction is operationally straightforward and proceeds under very mild conditions at room temperature in good to excellent yields (up to 99%) and regioselectivity.

  18. Synthesis of 2-Arylquinazolin-4(3H)-one Derivatives Catalyzed by Iodine in [bmim][

    Microsoft Academic Search

    Xiang-Shan Wang; Ke Yang; Mei-Mei Zhang; Chang-Sheng Yao

    2010-01-01

    Controlling selectivity of the reactions of aromatic aldehydes and 2-aminobenzamide in ionic liquid catalyzed by iodine at either room temperature or at 80 °C under nitrogen resulted in the synthesis of (E)-Schiff bases, 2,3-dihydro-2-arylquinazolin-4(1H)-one and 2-arylquinazolin-4(3H)-one derivatives, in excellent yields.

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

    E-print Network

    Paris-Sud XI, Université de

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

  20. Reconstitution and Characterization of Aminopyrrolnitrin Oxygenase, a Rieske N-Oxygenase That Catalyzes Unusual

    E-print Network

    Zhao, Huimin

    D) that catalyzes the unusual oxidation of an arylamine to an arylnitro group. PrnD from Pseudomonas fluorescens Pf5 fluorescens, and Pseudomonas cepacia and has broad spectrum antifungal activity (1­5). Biological activity)pyrrole) is produced by many Pseudomonads such as Pseudomonas pyrrocinia, Pseudomonas aureofaciens, Pseudomonas