Note: This page contains sample records for the topic calreticulin transacetylase catalyzed from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

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

PubMed

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

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

2

Acetoxy drug: Protein transacetylase catalyzed activation of human platelet nitric oxide synthase by polyphenolic peracetates  

Microsoft Academic Search

An enhanced intracellular level of Nitric oxide (NO) is essential to ameliorate several pathological conditions of heart and vasculature necessitating the activation of NOS. We have projected in this report the acetylation of eNOS by polyphenolic peracetates (PA) catalyzed by the novel enzyme acetoxy drug: protein transacetylase (TAase) discovered in our laboratory as an unambiguous way of activating NOS which

Pulkit Khurana; Ranju Kumari; Parag Vohra; Ajit Kumar; Seema; Garima Gupta; Hanumantharao G. Raj; Bilikere S. Dwarakanath; Virinder S. Parmar; Daman Saluja; Mridula Bose; Anjana Vij; Nabo K. Chaudhary; Jawahar S. Adhikari; Yogesh K. Tyagi; Ekta Kohli

2006-01-01

3

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

Microsoft Academic Search

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

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

2011-01-01

4

Protein acyltransferase function of purified calreticulin. Part 1: characterization of propionylation of protein utilizing propoxycoumarin as the propionyl group donor.  

PubMed

We have earlier reported that an endoplasmic reticulum luminal protein calreticulin (CR) mediated the acetylation of certain receptor proteins such as glutathione S-transferase (GST) by polyphenolic acetates, leading to irreversible inhibition. This function of calreticulin was termed calreticulin transacetylase. In this communication, we have demonstrated for the first time the ability of the purified recombinant calreticulin of a parasitic nematode Haemonchus contortus to transfer propionyl group from 7,8-Dipropoxy-4-methylcoumarin (DPMC) to recombinant Schistosoma japonicum glutathione S-transferase (rGST). Calreticulin transacetylase exhibited hyperbolic kinetics and yielded K(m) (140 microM) and V(max) (105 units) when the concentration of DPMC was varied keeping the concentration of rGST constant. rGST thus propionylated was found to positively interact with anti-acetyl lysine antibody. Also, the nanoscale LC-MS/MS analysis identified the propionylation sites on three lysine residues: Lys-11, -180 and -181 of rGST. These results highlight the transacylase function of calreticulin (CRTAase). PMID:20071373

Singh, Prabhjot; Ponnan, Prija; Krishnan, Shibu; Tyagi, Tapesh Kumar; Priya, Nivedita; Bansal, Seema; Scumaci, Domenica; Gaspari, Marco; Cuda, Giovanni; Joshi, Paritosh; Gambhir, Jasvinder Kaur; Saluja, Daman; Prasad, Ashok Kumar; Saso, Luciano; Rastogi, Ramesh Chandra; Parmar, Virinder Singh; Raj, Hanumantharao Guru

2010-01-12

5

Chemical and thermal unfolding of calreticulin.  

PubMed

Calreticulin is a soluble endoplasmic reticulum chaperone, which has a relatively low melting point due to its remarkable structure with a relatively high content of flexible structural elements. Using far ultraviolet circular dichroism (CD) spectroscopy and a fluorescent dye binding thermal shift assay, we have investigated the chemical and thermal stability of calreticulin. When the chemical stability of calreticulin was assessed, a midpoint for calreticulin unfolding was calculated to 3.0M urea using CD data at 222 nm. Using the fluorescent dye binding thermal shift assay, calreticulin was found to obtain a molten structure in urea concentrations between 1-1.5 M urea, and to unfold/aggregate at high and low pH values. The results demonstrated that the fluorescent dye binding assay could measure the thermal stability of calreticulin in aqueous buffers with results comparable to melting points obtained by other techniques. PMID:22998950

Duus, K; Larsen, N; Tran, T A T; Güven, E; Skov, L K; Jespersgaard, C; Gajhede, M; Houen, G

2013-05-01

6

Calreticulin signaling in health and disease.  

PubMed

Calreticulin is an endoplasmic reticulum Ca(2+) binding chaperone that has multiple functions inside and outside of the endoplasmic reticulum. It is involved in the quality control of newly synthesized proteins and glycoproteins, interacting with various other endoplasmic reticulum chaperones, specifically calnexin and ER protein of 57-kDa in the calreticulin/calnexin cycle. Calreticulin also plays a crucial role in regulating intracellular Ca(2+) homeostasis, associating calreticulin with a wide variety of signaling processes, such as cardiogenesis, adipocyte differentiation and cellular stress responses. The role of calreticulin outside of the endoplasmic reticulum is also extensive, including functions in wound healing and immunity. Therefore, calreticulin has important implications in health and disease. Signaling facts. PMID:22373697

Wang, Wen-An; Groenendyk, Jody; Michalak, Marek

2012-02-21

7

Platelet-activating factor acetylhydrolase and transacetylase activities in human plasma low-density lipoprotein.  

PubMed Central

In this study, we demonstrate the presence of a transacetylase activity in human plasma low-density lipoprotein (LDL) that transfers short-chain fatty acids from platelet-activating factor (PAF) and its close ether- and ester-linked analogues to ether/ester-linked lysophospholipids (lyso-PL). We show evidence that both PAF acetylhydrolase (PAF-AH) and transacetylase activities are inhibited to the same extent by serine esterase inhibitors, are resistant to heat treatment, and exhibit identical distributions in lipoprotein classes and in LDL subfractions. Additionally, the competitive inhibition of PAF-AH by lyso-PL, and the evidence that the recombinant PAF-AH also showed a similar transacetylase activity, suggest that PAF-AH is responsible for both activities. Using PAF as a donor molecule and lyso-PAF (1-O-alkyl-sn-glycero-3-phosphocholine) as an acceptor, the transacetylase activity showed typical allosteric kinetics, due to the positive co-operativity of the substrates, with apparent Vmax=19.6+/-3.4 nmol/min per mg of protein, apparent h=2.0+/-0.3 and apparent [S]0.5=9.4+/-2.3 microM at saturation for the concentration of lyso-PAF. The substrate specificity of the donor molecules was decreased by increasing the chain length of the acyl moiety in the sn-2 position of the glycerol. The ether linkage in the sn-1 position of the substrate was 30% more effective than the ester bond; cholesteryl acetate was inactive as an acetyl donor. The two acceptors tested, lyso-PAF and the ester-linked lyso-PC (1-acyl-sn-glycero-3-phosphocholine), showed similar specificity. Addition of exogenous lyso-PAF induced the transient formation of PAF-like aggregating activity predominantely in small dense LDL subfractions upon oxidation. We conclude that PAF-AH possesses both transacetylase and acetylhydrolase activities which remove PAF and its ether-linked analogues from LDL particles upon LDL oxidation. However, in atherogenic small dense LDL-5 particles, the transacetylase activity may acetylate extracellular lyso-PAF into biologically active PAF.

Tsoukatos, D C; Liapikos, T A; Tselepis, A D; Chapman, M J; Ninio, E

2001-01-01

8

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 9: comparison of acetoxy 4-methylcoumarins and other polyphenolic acetates reveal the specificity to acetoxy drug: protein transacetylase for pyran carbonyl group in proximity to the oxygen heteroatom.  

PubMed

The evidences for the possible enzymatic transfer of acetyl groups (catalyzed by a transacetylase localized in microsomes) from an acetylated compound (acetoxy-4-methylcoumarins) to enzyme proteins leading to profound modulation of their catalytic activities was cited in our earlier publications in this series. The investigations on the specificity for transacetylase (TA) with respect to the number and positions of acetoxy groups on the benzenoid ring of coumarin molecule revealed that acetoxy groups in proximity to the oxygen heteroatom (at C-7 and C-8 positions) demonstrate a high degree of specificity to TA. These studies were extended to the action of TA on acetates of other polyphenols, such as flavonoids and catechin with a view to establish the importance of pyran carbonyl group for the catalytic activity. The absolute requirement of the carbonyl group in the pyran ring of the substrate for TA to function was established by the observation that TA activity was hardly discernible when catechin pentacetate and 7-acetoxy-3,4-dihydro-2,2-dimethylbenzopyran (both lacking pyran ring carbonyl group) were used as the substrates. Further, the TA activity with flavonoid acetates was remarkably lower than that with acetoxycoumarins, thus suggesting the specificity for pyran carbonyl group in proximity to the oxygen heteroatom. The biochemical properties of flavonoid acetates, such as irreversible activation of NADPH cytochrome C reductase and microsome-catalyzed aflatoxin B(1) binding to DNA in vitro were found to be in tune with their specificity to TA. PMID:12413864

Singh, Ishwar; Kohli, Ekta; Raj, Hanumantharao G; Gyanda, Kapil; Jain, Sapan K; Tyagi, Yogesh K; Gupta, Garima; Kumari, Ranju; Kumar, Ajit; Pal, Giridhari; Prasad, Ashok K; Rastogi, Ramesh C; Olsen, Carl E; Jain, Subhash C; Parmar, Virinder S

2002-12-01

9

Characterization of the autoantigen calreticulin.  

PubMed

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

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

1991-11-01

10

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

PubMed

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

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

2006-12-29

11

Arrhythmia induced by spatiotemporal overexpression of calreticulin in the heart  

Microsoft Academic Search

Calreticulin (CRT) is a Ca2+-binding protein of the endoplasmic reticulum essential for cardiac development. For further investigation of the functional mechanism of calreticulin, we generated transgenic mice with spatiotemporal overexpression of calreticulin using a cre-loxP system. To elucidate the role of the protein in cardiogenesis, we adopted Nkx2.5-cre mice for heart specific overexpression. The overexpression of calreticulin was associated with

Kiyoko Hattori; Kimitoshi Nakamura; Yuichiro Hisatomi; Shirou Matsumoto; Misao Suzuki; Richard P. Harvey; Hiroki Kurihara; Shinzaburo Hattori; Tetsuro Yamamoto; Marek Michalak; Fumio Endo

2007-01-01

12

Calreticulin: not just another calcium-binding protein  

Microsoft Academic Search

In this paper we review some of the rapidly expanding information about calreticulin, a Ca(2+)-binding\\/storage protein of the endoplasmic reticulum. The emphasis is placed on the structure and function of calreticulin. We believe that calreticulin is a multifunctional Ca(2+)-binding protein and that distinct functional properties of the protein may be localized to each of the three structural domains of calreticulin.

P. D. Nash; Michal Opas; Marek Michalak

1994-01-01

13

Identification and localization of calreticulin in plant cells  

Microsoft Academic Search

Summary In the present study we have investigated the presence and distribution of calreticulin in plant protoplasts. Calreticulin was purified from plant homogenates using a selective ammonium sulfate precipitation procedure developed for the purification of mammalian calreticulins and shown to bind calcium in45Ca2+ overlay assays. The protein was localized to plant cell endoplasmic reticulum by the indirect immunofluorescence staining of

M. Opas; S. Tharin; R. E. Milner; M. Michalak

1996-01-01

14

Clinicopathological significance of calreticulin in breast invasive ductal carcinoma  

Microsoft Academic Search

Calreticulin is a chaperone protein located in the lumen of the endoplasmic reticulum. The association of calreticulin with pathological conditions such as autoimmune disorders and certain types of cancer have been reported. However, little is known about its role in the pathogenesis of breast cancer. The aim of this study was to determine the expression of calreticulin in vitro and

Zin-Mar Lwin; Chunhua Guo; Agus Salim; George Wai-Cheong Yip; Fook-Tim Chew; Jiang Nan; Aye Aye Thike; Puay-Hoon Tan; Boon-Huat Bay

2010-01-01

15

Calreticulin in the immune system: ins and outs.  

PubMed

Calreticulin is a calcium-binding chaperone that has several functions in the immune response. In the endoplasmic reticulum (ER), calreticulin facilitates the folding of major histocompatibility complex (MHC) class I molecules and their assembly factor tapasin, thereby influencing antigen presentation to cytotoxic T cells. Although calreticulin is normally ER-resident, it is found at the cell surface of living cancer cells and dying cells. Here, calreticulin promotes cellular phagocytic uptake. In tumor vaccine models, drugs that induce cell surface calreticulin confer enhanced tumor protection in an extracellular calreticulin-dependent manner. Much remains to be understood about the roles of calreticulin in these distinct functions. Further investigations are important towards advancing basic knowledge of glycoprotein-folding pathways, and towards developing new cancer therapeutic strategies. PMID:22959412

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

2012-09-07

16

Kinase-dependent adhesion to fibronectin: regulation by calreticulin.  

PubMed

We studied the phosphorylation (activation status) of c-Src and CaMKII in MEFs either wild type for calreticulin, calreticulin-null, or rescued with full-length calreticulin. We found that calreticulin-null cells were poorly spread on the substratum and formed few, if any, focal contacts. Fibronectin expression and deposition were lower in calreticulin-null MEFs compared to calreticulin-expressing cells, which also exhibited increased c-Src and CaMKII phosphorylation (activity). Plating MEFs on preformed fibronectin rescued the poor adhesive phenotype of calreticulin-null cells, and caused a decrease in c-Src Y418 phosphorylation (activity). c-Src inhibition caused the calreticulin-null MEFs to become well spread on the substratum and to make many prominent focal contacts. Calmodulin and CaMKII inhibition caused similar results, along with a notable increase in paxillin phosphorylation (activation). To test if the calcium storage function of calreticulin was responsible for these effects, we manipulated intracellular [Ca(2+)]. Lowering [Ca(2+)](ER) caused an increase in c-Src phosphorylation and a decrease in fibronectin abundance. Conversely, increasing [Ca(2+)] caused opposite effects. These results suggest that calreticulin regulates both the c-Src and calmodulin/CaMKII pathways, enabling cells to be better spread on the substratum by allowing greater fibronectin deposition and increased focal contact formation. PMID:18255058

Papp, Sylvia; Szabo, Eva; Kim, Hugh; McCulloch, Christopher A; Opas, Michal

2008-01-16

17

Maize calreticulin localizes preferentially to plasmodesmata in root apex.  

PubMed

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

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

1999-08-01

18

Differential modulation of SERCA2 isoforms by calreticulin.  

PubMed

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

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

1998-08-24

19

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

PubMed Central

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

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

2009-01-01

20

Transient Association of Calnexin and Calreticulin with Newly Synthesized G1 and G2 Glycoproteins of Uukuniemi Virus (Family Bunyaviridae)  

PubMed Central

The membrane glycoproteins G1 and G2 of Uukuniemi virus, a member of the Bunyaviridae family, are cotranslationally cleaved from a common precursor in the endoplasmic reticulum (ER). Here, we show that newly made G1 and G2 associate transiently with calnexin and calreticulin, two lectins involved in glycoprotein folding in the ER. Stable complexes between G1-G2 and calnexin or calreticulin could be immunoprecipitated after solubilization of virus-infected BHK21 cells with the detergents digitonin or Triton X-100. In addition, G1-G2-calnexin complexes could be recovered after solubilization with CHAPS {3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate}, while G1-G2-calreticulin complexes were not readily detected by using this detergent. Only endoglycosidase H-sensitive forms of G1 were found complexed with calnexin. Pulse-chase experiments showed that G1 and G2 associated with both chaperones transiently for up to 120 min. Sequential immunoprecipitations with anticalreticulin and anticalnexin antisera indicated that about 50% of newly synthesized G1 and G2 was associated with either calnexin or calreticulin. Our previous results have shown that newly synthesized G1 and G2 transiently interact also with the ER chaperone BiP and with protein disulfide isomerase (R. Persson and R. F. Pettersson, J. Cell Biol. 112:257–266, 1991). Taking all of this into consideration, we conclude that the folding of G1 and G2 in the ER is catalyzed by at least four different folding factors.

Veijola, Johanna; Pettersson, Ralf F.

1999-01-01

21

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...

22

Prevention of benzene-induced genotoxicity in bone marrow and lung cells: superiority of polyphenolic acetates to polyphenols.  

PubMed

Previous investigations carried out in our laboratory have highlighted that 7,8-diacetoxy-4-methylcoumarin demonstrates a mechanism-based inhibition of cytochrome P450 (Cyt-P450) activities such as microsome-mediated aflatoxin B1 (AFB1) epoxidation, dealkylation of alkylated resorufin, and toxicokinetics of benzene. 7,8-Diacetoxy-4-methylcoumarin, quercetin pentaacetate, and ellagic acid peracetate were also found to be effective in giving the protection of AFB1-induced genotoxicity in rat's bone marrow and lung cells possibly due to acetylation of Cyt-P450 apoprotein mediated by acetoxy drug: protein transacetylase. Later, this transacetylase was identified as calreticulin, and the acetyltransferase function of calreticulin was appropriately termed calreticulin transacetylase. In this communication, we have focused on the superiority of several classes of polyphenolic acetates to polyphenols in the modification of Cyt-P450-linked mixed function oxidases (MFOs) such as 7-ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin O-dealkylase (PROD). Special attention has also been focused on benzene-induced genotoxicity in bone marrow and lung cells. Results clearly indicated that polyphenolic acetates demonstrated time-dependent inhibition of Cyt-P450-linked MFOs, while parent polyphenols failed to demonstrate the same. Polyphenolic acetates were found to be more superior to polyphenols in preventing benzene-induced micronuclei formation. The pattern of inhibition of Cyt-P450-dependent MFOs and benzene-induced micronuclei formation by polyphenolic acetates was found in tune with their specificities to calreticulin transacetylase. These results further substantiated that inhibition of Cyt-P450-linked MFOs and benzene-induced genotoxicity in bone marrow and lung cells by polyphenolic acetates are mediated by the action of calreticulin transacetylase that catalyzes the acetylation of concerned proteins. PMID:21267547

Kumar, Ajit; Sushama, Anupam; Rohil, Vishwajeet; Manral, Sushma; Gangopadhyay, Sukanya; Prasad, Ashok K; Raj, Hanumantharao G; Parmar, Virender S

2011-01-26

23

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

PubMed Central

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

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

2011-01-01

24

Lipoyl content and other properties of the protein X and the transacetylase components of the pyruvate dehydrogenase complex  

SciTech Connect

Previous work demonstrated by structural and immunological techniques that protein X (X) was distinct from the transacetylase (E2) but that regions of X and E2 (specifically including the portions acetylated) were similar. Trypsin cleaved X and E2 into large domains giving acetylated portions with apparent M/sub r/ values of approx.20 kdal and approx.38 kdal, respectively. Purified (denatured) E2 and X subunits were prepared and amino acid compositions determined. Reduced subunits were reacted with FDNB and acid hydrolyzed. Bis(DNP)dihydrolipoic was extracted into ethylacetate and quantitated by HPLC (epsilon = 25 O.D.mM/sup -1/cm/sup -1/ at 340 nm) and the levels normalized based on the amino acid analysis of the acid hydrolysates. E2 and X were estimated to contain about 1 lipoyl moiety per subunit. Following dihydrolipoyl dehydrogenase-dependent NADH reduction of E2-X, 1.5-2 /sup 14/C-NEM per subunit were incorporated into E2 and X consistent with reduction of one lipoyl moiety per subunit. Incorporation into E2-X subcomplex of > 90 acetyl groups per molecule of subcomplex led to > 1.5 acetyl group incorporated per X and per E2 subunit and nearly eliminated NADH-dependent incorporation of /sup 14/C-NEM into these subunits suggesting diacetyl moieties were formed. Consistent with that possibility, acetylation to high levels yielded rapid and slowly exchanging acetyl groups on both E2 and X.

Radke, G.A.; Rahmatullah, M.; Jilka, J.M; Roche, T.E.

1986-05-01

25

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

Microsoft Academic Search

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

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

2011-01-01

26

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

PubMed Central

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.

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

27

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

PubMed

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

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

1991-12-01

28

Inhibition of nuclear hormone receptor activity by calreticulin  

Microsoft Academic Search

WE have shown that a polypeptide of Mr 60,000 (60K) that shares N-terminal homology with a calcium-binding protein, calreticulin, can bind to an amino-acid sequence motif, KXGFFKR, found in the cytoplasmic domains of all integrin alpha-subunits1. The homologous amino-acid sequence, KXFFKR (where X is either G, A or V), is also present in the DNA-binding domain of all known members

Shoukat Dedhar; Paul S. Rennie; Mary Shago; Chung-Yee Leung Hagesteijn; Huiling Yang; Jorge Filmus; Robert G. Hawley; Nicholas Bruchovsky; Helen Cheng; Robert J. Matusik; Vincent Giguère

1994-01-01

29

Analyses of carbohydrate binding property of lectin-chaperone calreticulin  

Microsoft Academic Search

Calreticulin (CRT) is a soluble molecular chaperone of the endoplasmic reticulum. It is a lectin that promotes the folding of proteins carrying N-linked glycans. Recent investigations have revealed that glucosylated high-mannose-type glycans are employed as key elements in this process. Here, we performed quantitative analyses of the interaction of CRT with various disaccharides, including fluorine-substituted analogues using a quartz-crystal microbalance

Atsushi Tatami; Yung-Son Hon; Ichiro Matsuo; Maki Takatani; Hiroyuki Koshino; Yukishige Ito

2007-01-01

30

Characterization of calreticulin as a protein interacting with protein kinase C.  

PubMed Central

A protein kinase C (PKC)-binding protein was purified to homogeneity from the Triton-insoluble fraction from rat hepatocytes homogenates. The protein was identified as the mature calreticulin chain by N-terminal amino acid sequencing and by its immunoreactivity with anti-calreticulin antibody raised against the C-terminal KDEL (single-letter code) sequence. The calculated molecular mass was 46. 6 kDa but the protein migrates in SDS/PAGE as a doublet with apparent molecular masses of 60 and 55 kDa. Studies in vitro with purified calreticulin with the use of an overlay assay approach demonstrated that it binds to activated PKC isoenzymes expressed in rat hepatocytes. Phosphorylation of purified calreticulin with a PKC isoenzyme-specific immune complex kinase assay showed that it is also a very good substrate for all PKC isoforms in vitro. The treatment of intact cells with phorbol ester or with adrenaline (epinephrine) plus propranolol increased calreticulin phosphorylation, which was blocked by the pretreatment of cells with the PKC-specific inhibitor Ro 31-8220. The analysis of calreticulin immunoprecipitates from control or treated cells indicated that PKCalpha, PKCbeta, PKCtheta;, PKCzeta and PKCmu, but not PKCdelta or PKCepsilon, co-immunoprecipitated with calreticulin. Taken together, our results indicate that PKC interacts in vivo with calreticulin and suggest that they can operate in common signalling pathways.

Rendon-Huerta, E; Mendoza-Hernandez, G; Robles-Flores, M

1999-01-01

31

Calreticulin is a negative regulator of bronchial smooth muscle cell proliferation.  

PubMed

Background. Calreticulin controls the C/EBP?p42/p30 at the translational level trough a cis-regulatory CNG rich loop in the CEBPA mRNA. We determined the effects of steroids and long-acting beta-agonists on the p42/p30 ratio and on calreticulin expression in primary human bronchial smooth muscle (BSM) cells. Methods. The effects of budesonide (10(-8)?M) and formoterol (10(-8)?M) were studied in BSM cells pre-treated with siRNA targeting calreticulin. The expression of C/EBP? and calreticulin was determined by immuno-blotting. Automated cell counts were performed to measure proliferation. Results. All tested BSM cell lines (n = 5) expressed C/EBP? and calreticulin. In the presence of 5% FBS, the p42/p30 ratio significantly decreased (n = 3, P < 0.05) and coincided with BSM cell proliferation. High levels of calreticulin were associated with a decreased p42/p30 isoform ratio. FBS induced the expression of calreticulin (n = 3, P < 0.05), which was further increased by formoterol. siRNA targeting calreticulin increased the p42/p30 ratio in non-stimulated BSM cells and significantly inhibited the proliferation of PDGF-BB-stimulated BSM cells (n = 5, P < 0.05). Neither budesonide nor formoterol restored the p42 isoform expression. Conclusions. Our data show calreticulin is a negative regulator of C/EBP? protein expression in BSM cells. Modulation of calreticulin levels may provide a novel target to reduce BSM remodeling. PMID:22500186

Miglino, Nicola; Roth, Michael; Lardinois, Didier; Tamm, Michael; Borger, Peter

2012-02-21

32

Calreticulin Is a Negative Regulator of Bronchial Smooth Muscle Cell Proliferation  

PubMed Central

Background. Calreticulin controls the C/EBP?p42/p30 at the translational level trough a cis-regulatory CNG rich loop in the CEBPA mRNA. We determined the effects of steroids and long-acting beta-agonists on the p42/p30 ratio and on calreticulin expression in primary human bronchial smooth muscle (BSM) cells. Methods. The effects of budesonide (10?8?M) and formoterol (10?8?M) were studied in BSM cells pre-treated with siRNA targeting calreticulin. The expression of C/EBP? and calreticulin was determined by immuno-blotting. Automated cell counts were performed to measure proliferation. Results. All tested BSM cell lines (n = 5) expressed C/EBP? and calreticulin. In the presence of 5% FBS, the p42/p30 ratio significantly decreased (n = 3, P < 0.05) and coincided with BSM cell proliferation. High levels of calreticulin were associated with a decreased p42/p30 isoform ratio. FBS induced the expression of calreticulin (n = 3, P < 0.05), which was further increased by formoterol. siRNA targeting calreticulin increased the p42/p30 ratio in non-stimulated BSM cells and significantly inhibited the proliferation of PDGF-BB-stimulated BSM cells (n = 5, P < 0.05). Neither budesonide nor formoterol restored the p42 isoform expression. Conclusions. Our data show calreticulin is a negative regulator of C/EBP? protein expression in BSM cells. Modulation of calreticulin levels may provide a novel target to reduce BSM remodeling.

Miglino, Nicola; Roth, Michael; Lardinois, Didier; Tamm, Michael; Borger, Peter

2012-01-01

33

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

PubMed Central

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.

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

2009-01-01

34

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

PubMed Central

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

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

2011-01-01

35

Decoded Calreticulin-Deficient Embryonic Stem Cell Transcriptome Resolves Latent Cardiophenotype  

PubMed Central

Genomic perturbations that challenge normal signaling at the pluripotent stage may trigger unforeseen ontogenic aberrancies. Anticipatory systems biology identification of transcriptome landscapes that underlie latent phenotypes would offer molecular diagnosis before the onset of symptoms. The purpose of this study was to assess the impact of calreticulin-deficient embryonic stem cell transcriptomes on molecular functions and physiological systems. Bioinformatic surveillance of calreticulin-null stem cells, a monogenic insult model, diagnosed a disruption in transcriptome dynamics, which re-prioritized essential cellular functions. Calreticulin-calibrated signaling axes were uncovered, and network-wide cartography of undifferentiated stem cell transcripts suggested cardiac manifestations. Calreticulin-deficient stem cell-derived cardiac cells verified disorganized sarcomerogenesis, mitochondrial paucity, and cytoarchitectural aberrations to validate calreticulin-dependent network forecasts. Furthermore, magnetic resonance imaging and histopathology detected a ventricular septal defect, revealing organogenic manifestation of calreticulin deletion. Thus, bioinformatic deciphering of a primordial calreticulin-deficient transcriptome decoded at the pluripotent stem cell stage a reconfigured multifunctional molecular registry to anticipate predifferentiation susceptibility toward abnormal cardiophenotype.

Faustino, Randolph S.; Chiriac, Anca; Niederlander, Nicolas J.; Nelson, Timothy J.; Behfar, Atta; Mishra, Prasanna K.; Macura, Slobodan; Michalak, Marek; Terzic, Andre; Perez-Terzic, Carmen

2011-01-01

36

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

PubMed

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

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

2011-03-01

37

NMR structure of the calreticulin P-domain  

PubMed Central

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

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

2001-01-01

38

Suppressive Role of Androgen-Response Gene Calreticulin in Prostate Cancer.  

National Technical Information Service (NTIS)

Androgens are intimately associated with prostate cancer progression. We have previously identified more than 24 androgen-response genes. One of the genes encodes calreticulin, a highly conserved protein with demonstrated%functions in intracellular Ca% ho...

Z. Wang

2002-01-01

39

Suppression Role of Androgen-Response Gene Calreticulin in Prostate Cancer.  

National Technical Information Service (NTIS)

Androgens are intimately associated with prostate cancer progression. We have previously identified more than 24 androgen-response genes. One of the genes encodes calreticulin, a highly conserved protein with demonstrated functions in intracellular Ca(++)...

Z. Wang

2003-01-01

40

Suppressive Role of Androgen-Response Gene Calreticulin in Prostate Cancer.  

National Technical Information Service (NTIS)

Androgens are intimately associated with prostate cancer progression. One of the androgen-response genes encodes calreticulin, a highly conserved protein with demonstrated functions in intracellular Ca++ homeostasis, cell adhesion, chaperoning, and gene e...

Z. Wang

2004-01-01

41

Calreticulin Is the Major Ca 2+ Storage Protein in the Endoplasmic Reticulum of the Pea Plant ( Pisum sativum)  

Microsoft Academic Search

A 56kDa protein with high similarity in its N-terminal amino acid sequence to animal calreticulin and 100% homology with the N-terminal amino acids of spinach calreticulin has been identified in seeds of the pea plant (Pisum sativum). A new purification procedure is described by which the calreticulin-like protein was selectively solubilized by incubation with deoxycholate and HgCl2 from microsomes enriched

A. M. Hassan; C. Wesson; W. R. Trumble

1995-01-01

42

Regulation of peripheral T cell activation by calreticulin  

PubMed Central

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

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

2006-01-01

43

Antiangiogenic and Antitumor Effects of Trypanosoma cruzi Calreticulin  

PubMed Central

Background In Latin America, 18 million people are infected with Trypanosoma cruzi, the agent of Chagas' disease, with the greatest economic burden. Vertebrate calreticulins (CRT) are multifunctional, intra- and extracellular proteins. In the endoplasmic reticulum (ER) they bind calcium and act as chaperones. Since human CRT (HuCRT) is antiangiogenic and suppresses tumor growth, the presence of these functions in the parasite orthologue may have consequences in the host/parasite interaction. Previously, we have cloned and expressed T. cruzi calreticulin (TcCRT) and shown that TcCRT, translocated from the ER to the area of trypomastigote flagellum emergence, promotes infectivity, inactivates the complement system and inhibits angiogenesis in the chorioallantoid chicken egg membrane. Most likely, derived from these properties, TcCRT displays in vivo inhibitory effects against an experimental mammary tumor. Methodology and Principal Findings TcCRT (or its N-terminal vasostatin-like domain, N-TcCRT) a) Abrogates capillary growth in the ex vivo rat aortic ring assay, b) Inhibits capillary morphogenesis in a human umbilical vein endothelial cell (HUVEC) assay, c) Inhibits migration and proliferation of HUVECs and the human endothelial cell line Eahy926. In these assays TcCRT was more effective, in molar terms, than HuCRT: d) In confocal microscopy, live HUVECs and EAhy926 cells, are recognized by FITC-TcCRT, followed by its internalization and accumulation around the host cell nuclei, a phenomenon that is abrogated by Fucoidin, a specific scavenger receptor ligand and, e) Inhibits in vivo the growth of the murine mammary TA3 MTXR tumor cell line. Conclusions/Significance We describe herein antiangiogenic and antitumor properties of a parasite chaperone molecule, specifically TcCRT. Perhaps, by virtue of its capacity to inhibit angiogenesis (and the complement system), TcCRT is anti-inflammatory, thus impairing the antiparasite immune response. The TcCRT antiangiogenic effect could also explain, at least partially, the in vivo antitumor effects reported herein and the reports proposing antitumor properties for T. cruzi infection.

Lopez, Nandy C.; Valck, Carolina; Ramirez, Galia; Rodriguez, Margarita; Ribeiro, Carolina; Orellana, Juana; Maldonado, Ismael; Albini, Adriana; Anacona, Daniel; Lemus, David; Aguilar, Lorena; Schwaeble, Wilhelm; Ferreira, Arturo

2010-01-01

44

Alternative chaperone machinery may compensate for calreticulin/calnexin deficiency in Caenorhabditis elegans.  

PubMed

Proper folding and maintenance of the native structure are central to protein function and are assisted by a family of proteins called chaperones. Calreticulin and calnexin are ER resident chaperones well conserved from worm to human. Calreticulin/calnexin knock-out mice exhibit a severe phenotype, whereas in Caenorhabditis elegans, calreticulin [crt-1(jh101)]- and calnexin [cnx-1(nr2009)]-null mutant worms exhibit only a mild phenotype, suggesting the possible existence of alternative chaperone machinery that can compensate for the deficiency of calreticulin and/or calnexin. In order to rapidly identify the compensatory chaperone components involved in this process, we analyzed the proteome of crt-1(jh101) mutants and [crt-1(jh101);cnx-1(nr2009)] double mutants. When grown at 20 degrees C, we found that five proteins were up-regulated and two proteins were down-regulated in crt-1(jh101) mutants; nine proteins were up-regulated and five proteins were down-regulated in [crt-1(jh101);cnx-1(nr2009)] double mutants. In addition, elevation of the cultivation temperature to 25 degrees C, which is still permissive to growth but causes specific defects in mutants, led to the identification of several additional proteins. Interestingly, the consistent increment of heat shock protein-70 family members (hsp70) together with protein disulfide isomerase (PDI) at all the examined conditions suggests the possible compensatory function imparted by hsp70 and PDI family members in the absence of calreticulin and/or calnexin. PMID:16404716

Lee, Wonhae; Kim, Ki Ra; Singaravelu, Gunasekaran; Park, Byung-Jae; Kim, Do Han; Ahnn, Joohong; Yoo, Yung Joon

2006-02-01

45

Structural and Functional Relationships between the Lectin and Arm Domains of Calreticulin*  

PubMed Central

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

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

2011-01-01

46

Calreticulin Enhances Porcine Wound Repair by Diverse Biological Effects  

PubMed Central

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

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

2008-01-01

47

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

PubMed Central

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

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

2010-01-01

48

Calreticulin Binds to Gentamicin and Reduces Drug-Induced Ototoxicity  

PubMed Central

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.

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

2011-01-01

49

Calreticulin regulates transforming growth factor-?-stimulated extracellular matrix production.  

PubMed

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 Ca(2+) 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 Ca(2+) signaling is important for induction of ECM. CRT-/- MEFs failed to increase intracellular Ca(2+) 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 Ca(2+)-dependent pathways as a critical molecular link between ER stress and TGF-? fibrotic signaling. PMID:23564462

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

2013-04-05

50

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

PubMed Central

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

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

2002-01-01

51

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

PubMed Central

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

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

1995-01-01

52

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

PubMed Central

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

2013-01-01

53

Functional analysis of recombinant calreticulin fragment 39-272: implications for immunobiological activities of calreticulin in health and disease.  

PubMed

Although calreticulin (CRT) is a major Ca(2+)-binding luminal resident protein, it can also appear on the surface of various types of cells and it functions as an immunopotentiating molecule. However, molecular mechanisms underlying the potent immunobiological activity of cell surface CRT are still unclear. In the present study, a recombinant fragment (rCRT/39-272) covering the lectin-like N domain and partial P domain of murine CRT has been expressed in Escherichia coli. The affinity-purified rCRT/39-272 assembles into homodimers and oligomers in solution and exhibits high binding affinity to various glycans, including carrageenan, alginic acids, and hyaluronic acids. Functionally, rCRT/39-272 is capable of driving the activation and maturation of B cells and cytokine production by macrophages in a TLR-4-dependent manner in vitro. It specifically binds recombinant mouse CD14, but not BAFFR and CD40. It is also able to trigger Ig class switching by B cells in the absence of T cell help both in vitro and in vivo. Furthermore, this fragment of CRT exhibits strong adjuvanticity when conjugated to polysaccharides or expressed as part of a fusion protein. Soluble CRT can be detected in the sera of patients with rheumatoid arthritis or systemic lupus erythematosus, but not in healthy subjects. We argue that CRT, either on the membrane surface of cells or in soluble form, is a potent stimulatory molecule to B cells and macrophages via the TLR-4/CD14 pathway and plays important roles in the pathogenesis of autoimmune diseases. PMID:20855873

Hong, Chao; Qiu, Xiang; Li, Yue; Huang, Qianrong; Zhong, Zhaoyan; Zhang, Yan; Liu, Xiangyuan; Sun, Lin; Lv, Ping; Gao, Xiao-Ming

2010-09-20

54

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

PubMed Central

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

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

2009-01-01

55

Calcium-induced protein phosphorylation and changes in levels of calmodulin and calreticulin in maize sperm cells  

Microsoft Academic Search

To examine possible calcium (Ca2+)-mediated prefertilization events in male gametes of higher plants, we studied protein phosphorylation and the Ca2+-binding proteins, calmodulin and calreticulin, in sperm cells isolated from maize (Zea mays L.) pollen in the presence and absence of Ca2+. Using immunoblotting, we detected calmodulin and calreticulin and Ca2+-induced variations. Exposure of sperm cells to 1?mM Ca2+ for 1?h

Connie M. Williams; Guichang Zhang; Marek Michalak; David D. Cass

1997-01-01

56

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

PubMed Central

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

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

1999-01-01

57

Calreticulin inhibits glucocorticoid– but not cAMP–sensitive expression of tyrosine aminotransferase gene in cultured McA–RH7777 hepatocytes  

Microsoft Academic Search

Calreticulin is a ubiquitously expressed Ca2+ binding protein of the endoplasmic reticulum which inhibits DNA binding and transcriptional activation by steroid hormone receptors. In this study the effects of calreticulin on tyrosine aminotransferase (TAT) gene expression in cultured McA–RH7777 hepatocytes was investigated. McA–RH7777 cells were stably transfected with calreticulin expression vector to generate cells overexpressing the protein. The transcriptional activity

Kimberly Burns; Michal Opas; Marek Michalak

1997-01-01

58

Effects of prenatal glucocorticoid exposure on cardiac calreticulin and calsequestrin protein expression during early development and in adulthood.  

PubMed Central

Overexpression of the conserved Ca(2+)-binding proteins calreticulin and calsequestrin impairs cardiac function, leading to premature death. Calreticulin is vital for embryonic development, but also impairs glucocorticoid action. Glucocorticoid overexposure during late fetal life causes intra-uterine growth retardation and programmed hypertension in adulthood. To determine whether intra-uterine growth retardation or programmed hypertension was associated with altered calreticulin or calsequestrin expression, effects of prenatal glucocorticoid overexposure (maternal dexamethasone treatment on days 15-21 of pregnancy) were examined during fetal life and postnatal development until adulthood (24 weeks). Dexamethasone (100 or 200 microg/kg of maternal body weight) was administered via osmotic pump. Calreticulin was detected as a 55 kDa band and calsequestrin as 55 and 63 kDa bands in 21 day fetal hearts. Only the 55 kDa calsequestrin band was detected postnatally. Prenatal glucocorticoid overexposure at the higher dose decreased calreticulin protein expression (26%; P <0.05) but increased calsequestrin protein expression, both 55 and 63 kDa bands, by 87% ( P <0.01) and 78% ( P <0.01); only the 55 kDa calsequestrin band was increased at the lower dose (66%; P <0.05). Offspring of dams treated at the lower dexamethasone dose were studied further. In control offspring, cardiac calreticulin protein expression declined between 2 and 3 weeks of age, and remained suppressed until adulthood. Cardiac calsequestrin protein expression increased 2-fold between fetal day 21 and postnatal day 1 and continued to increase until adulthood, at which time it was 3.4-fold higher ( P <0.001). Prenatal dexamethasone exposure minimally affected postnatal calsequestrin protein expression, but the postnatal decline in calreticulin protein expression was abrogated and calreticulin protein expression in adulthood was 2.2-fold increased ( P <0.001) compared with adult controls. In view of the known associations between cardiac calreticulin overexpression and impaired cardiac function, targeted up-regulation of calreticulin may contribute to the increased risk of adult heart disease introduced as a result of prenatal overexposure to glucocorticoids.

Langdown, Maria L; Holness, Mark J; Sugden, Mary C

2003-01-01

59

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

Microsoft Academic Search

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

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

2002-01-01

60

Cloning and partial characterization of a Boophilus microplus (Acari: Ixodidae) calreticulin  

Microsoft Academic Search

We report the cloning, sequence characterization and expression analysis of a calreticulin (CRT) coding cDNA of Boophilus microplus. CRT is a calcium-binding protein involved in multiple cell functions and possibly implicated in parasites host immune system evasion. The CRT cDNA sequence and its molecular characterization are described. Sequence similarity and phylogenetic analyses indicate a close relationship to other arthropod CRT

Carlos Alexandre Sanchez Ferreira; Itabajara Da Silva Vaz; Sérgio Silva da Silva; Karen L Haag; Jesus G Valenzuela; Aoi Masuda

2002-01-01

61

Nuclear export of the glucocorticoid receptor is accelerated by cell fusion-dependent release of calreticulin.  

PubMed

Nucleocytoplasmic exchange of nuclear hormone receptors is hypothesized to allow for rapid and direct interactions with cytoplasmic signaling factors. In addition to recycling between a naïve, chaperone-associated cytoplasmic complex and a liganded chaperone-free nuclear form, the glucocorticoid receptor (GR) has been observed to shuttle between nucleus and cytoplasm. Nuclear export of GR and other nuclear receptors has been proposed to depend on direct interactions with calreticulin, which is predominantly localized to the lumen of the endoplasmic reticulum. We show that rapid calreticulin-mediated nuclear export of GR is a specific response to transient disruption of the endoplasmic reticulum that occurs during polyethylene glycol-mediated cell fusion. Using live and digitonin-permeabilized cells we demonstrate that, in the absence of cell fusion, GR nuclear export occurs slowly over a period of many hours independent of direct interaction with calreticulin. Our findings temper expectations that nuclear receptors respond rapidly and directly to cytoplasmic signals in the absence of additional regulatory control. These results highlight the importance of verifying findings of nucleocytoplasmic trafficking using techniques in addition to heterokaryon cell fusion. PMID:12869547

Walther, Rhian F; Lamprecht, Claudia; Ridsdale, Andrew; Groulx, Isabelle; Lee, Stephen; Lefebvre, Yvonne A; Haché, Robert J G

2003-07-17

62

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

PubMed Central

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.

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

1994-01-01

63

The calcium-binding protein calreticulin is a major constituent of lytic granules in cytolytic T lymphocytes  

PubMed Central

Cytolytic T lymphocytes (CTL), natural killer cells, and lymphokine- activated killer (LAK) cells are cytolytic cells known to release the cytolytic protein perforin and a family of proteases, named granzymes, from cytoplasmic stores upon interaction with target cells. We now report the purification of an additional major 60-kD granule-associated protein (grp 60) from human LAK cells and from mouse cytolytic T cells. The NH2-terminal amino acid sequence of the polypeptide was found to be identical to calreticulin. Calreticulin is a calcium storage protein and carries a COOH-terminal KDEL sequence, known to act as a retention signal for proteins destined to the lumen of the endoplasmic reticulum. In CTLs, however, calreticulin colocalizes with the lytic perforin to the lysosome-like secretory granules, as confirmed by double label immunofluorescence confocal microscopy. Moreover, when the release of granule-associated proteins was triggered by stimulation of the T cell receptor complex, calreticulin was released along with granzymes A and D. Since perforin is activated and becomes lytic in the presence of calcium, we propose that the role of calreticulin is to prevent organelle autolysis due to the protein's calcium chelator capacity.

1993-01-01

64

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

PubMed

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

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

2013-08-08

65

Differential requirement of unfolded protein response pathway for calreticulin expression in Caenorhabditis elegans.  

PubMed

Accumulation of unfolded proteins in the endoplasmic reticulum triggers the unfolded protein response (UPR) pathway, which increases the expression of chaperones to maintain the homeostasis. Calreticulin is a calcium-binding chaperone located in the lumen of endoplasmic reticulum (ER). Here we show that in response to a UPR inducing reagent, tunicamycin, the expression of calreticulin (crt-1) is specifically up-regulated in Caenorhabditis elegans. Tunicamycin (TM) induced expression of the crt-1 requires IRE-1 and XBP-1 but is ATF-6 and PEK-1 independent. Analysis of the crt-1 promoter reveals a putative XBP-1 binding site at the -284 to -278 bp region, which was shown to be necessary for TM-mediated induction. Genetic analysis of crt-1 mutants and mutants of UPR pathway genes show various degrees of developmental arrest upon TM treatment. Our results suggest that the TM-induced UPR pathway culminates in the up-regulation of crt-1, which protects the worm from deleterious accumulation of unfolded proteins in the ER. Knockdown of the crt-1, pdi-2, or pdi-3 increased the crt-1 expression, whereas knockdown of the hsp-3 or hsp-4 did not have any effect on crt-1 expression, indicating the existence of complex compensatory networks to cope up with ER stress. PMID:17651753

Lee, Dukgyu; Singaravelu, Gunasekaran; Park, Byung-Jae; Ahnn, Joohong

2007-07-03

66

Transient Dissociation of Polyribosomes and Concurrent Recruitment of Calreticulin and Calmodulin Transcripts in Gravistimulated Maize Pulvini1  

PubMed Central

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

Heilmann, Ingo; Shin, Jai; Huang, Jamie; Perera, Imara Y.; Davies, Eric

2001-01-01

67

Assessment of Roles for Calreticulin in the Cross-Presentation of Soluble and Bead-Associated Antigens  

PubMed Central

Antigen cross-presentation involves the uptake and processing of exogenously derived antigens and their assembly with major histocompatibility complex (MHC) class I molecules. Antigen presenting cells (APC) load peptides derived from the exogenous antigens onto MHC class I molecules for presentation to CD8 T cells. Calreticulin has been suggested to mediate and enhance antigen cross-presentation of soluble and cell-derived antigens. In this study, we examined roles for calreticulin in cross-presentation of ovalbumin using a number of models. Our findings indicate that calreticulin does not enhance in vitro cross-presentation of an ovalbumin-derived peptide, or of fused or bead-associated ovalbumin. Additionally, in vivo, calreticulin fusion or co-conjugation does not enhance the efficiency of CD8 T cell activation by soluble or bead-associated ovalbumin either in wild type mice or in mice lacking Toll-like receptor 4 (TLR4). Furthermore, we detect no significant differences in cross-presentation efficiencies of glycosylated vs. non-glycosylated forms of ovalbumin. Together, these results point to the redundancies in pathways for uptake of soluble and bead-associated antigens.

Del Cid, Natasha; Shen, Lianjun; BelleIsle, Janice; Raghavan, Malini

2012-01-01

68

Calreticulin-STAT3 Signaling Pathway Modulates Mitochondrial Function in a Rat Model of Furazolidone-Induced Dilated Cardiomyopathy  

PubMed Central

Background Calreticulin is a Ca2+-binding chaperone of the endoplasmic reticulum which regulates the signal transducer and activator of transcription 3 (STAT3). The effects of the calreticulin-STAT3 signaling pathway on cardiac mitochondria and on the progress of dilated cardiomyopathy (DCM) are still unclear. Methods and Results The DCM model was generated in rats by the daily oral administration of furazolidone. Echocardiographic and hemodynamic studies demonstrated enlarged LV dimensions and reduced systolic and diastolic functions at thirty weeks after the first furazolidone administration. Morphometric analysis showed significant myocardial degeneration, interstitial fibrosis, and mitochondrial swelling with fractured or dissolved cristae in the model group. Compared with the control group, the mitochondrial membrane potential (MMP) level of the freshly isolated cardiac mitochondria and the enzyme activities of cytochrome c oxidase and succinate dehydrogenase in the model group were significantly decreased (P<0.05). Real-time PCR and western-blot revealed the increased expression of calreticulin associated with decreased activity of STAT3 in the model group. When cultured neonatal rat cardiomyocytes were exposed to furazolidone, a dose-dependent decrease in cell viability and MMP, and the increase of apoptosis rate were observed. The mRNA and protein expression of CRT gradually increased with the increase of furazolidone concentration, associated with a gradual decrease of the STAT3 phosphorylation level both in the whole cell and mitochondrial fraction. When calreticulin was knocked down with siRNA in cardiomyocytes, these changes of cardiomyocytes and mitochondria induced by furazolidone were significantly attenuated. Conclusions A rat model of DCM induced by furazolidone is successfully established. The calreticulin-STAT3 signaling pathway is involved in cardiac mitochondrial injury and the progress of furazolidone induced DCM.

Zhang, Ming; Wei, Jin; Shan, Hu; Wang, Hao; Zhu, Yanhe; Xue, Jiahong; Lin, Lin; Yan, Rui

2013-01-01

69

Folding of thyroglobulin in the calnexin/calreticulin pathway and its alteration by loss of Ca2+ from the endoplasmic reticulum.  

PubMed Central

During its initial folding in the endoplasmic reticulum (ER), newly synthesized thyroglobulin (Tg) is known to interact with calnexin and other ER molecular chaperones, but its interaction with calreticulin has not been examined previously. In the present study, we have investigated the interactions of endogenous Tg with calreticulin and with several other ER chaperones. We find that, in FRTL-5 and PC-Cl3 cells, calnexin and calreticulin interact with newly synthesized Tg in a carbohydrate-dependent manner, with largely overlapping kinetics that are concomitant with the maturation of Tg intrachain disulphide bonds, preceding Tg dimerization and exit from the ER. Calreticulin co-precipitates more newly synthesized Tg than does calnexin; however, using two different experimental approaches, calnexin and calreticulin were found in ternary complexes with Tg, making this the first endogenous protein reported in ternary complexes with calnexin and calreticulin in the ER of live cells. Depletion of Ca(2+) from the ER elicited by thapsigargin (a specific inhibitor of ER Ca(2+)-ATPases) results in retention of Tg in this organelle. Interestingly, thapsigargin treatment induces the premature exit of Tg from the calnexin/calreticulin cycle, while stabilizing and prolonging interactions of Tg with BiP (immunoglobulin heavy chain binding protein) and GRP94 (glucose-regulated protein 94), two chaperones whose binding is not carbohydrate-dependent. Our results suggest that calnexin and calreticulin, acting in ternary complexes with a large glycoprotein substrate such as Tg, might be engaged in the folding of distinct domains, and indicate that lumenal Ca(2+) strongly influences the folding of exportable glycoproteins, in part by regulating the balance of substrate binding to different molecular chaperone systems within the ER.

Di Jeso, Bruno; Ulianich, Luca; Pacifico, Francesco; Leonardi, Antonio; Vito, Pasquale; Consiglio, Eduardo; Formisano, Silvestro; Arvan, Peter

2003-01-01

70

Calreticulin-dimerization induced by post-translational arginylation is critical for stress granules scaffolding.  

PubMed

Protein arginylation mediated by arginyl-tRNA protein transferase is a post-translational modification that occurs widely in biology, it has been shown to regulate protein and properties and functions. Post-translational arginylation is critical for embryogenesis, cardiovascular development and angiogenesis but the molecular effects of proteins arginylated in vivo are largely unknown. In the present study, we demonstrate that arginylation reduces CRT (calreticulin) thermostability and induces a greater degree of dimerization and oligomerization. R-CRT (arginylated calreticulin) forms disulfide-bridged dimers that are increased in low Ca(2+) conditions at physiological temperatures, a similar condition to the cellular environment that it required for arginylation of CRT. Moreover, R-CRT self-oligomerizes through non-covalent interactions that are enhanced at temperatures above 40 °C, condition that mimics the heat shock treatment where R-CRT is the only isoespecies of CRT that associates in cells to SGs (stress granules). We show that in cells lacking CRT the scaffolding of larger SGs is impaired; the transfection with CRT (hence R-CRT expression) restores SGs assembly whereas the transfection with CRT mutated in Cys146 does not. Thus, R-CRT disulfide-bridged dimers (through Cys146) are essential for the scaffolding of larger SGs under heat shock, although these dimers are not required for R-CRT association to SGs. The alteration in SGs assembly is critical for the normal cellular recover of cells after heat induced stress. We conclude that R-CRT is emerging as a novel protein that has an impact on the regulation of SGs scaffolding and cell survival. PMID:23567256

Carpio, Marcos A; Decca, María B; Lopez Sambrooks, Cecilia; Durand, Edith S; Montich, Guillermo G; Hallak, Marta E

2013-04-06

71

Characterization of DNA vaccines encoding the domains of calreticulin for their ability to elicit tumor-specific immunity and antiangiogenesis  

Microsoft Academic Search

Antigen-specific cancer immunotherapy and antiangiogenesis are feasible strategies for cancer therapy because they can potentially treat systemic tumors at multiple sites in the body while discriminating between neoplastic and non-neoplastic cells. We have previously developed a DNA vaccine encoding calreticulin (CRT) linked to human papillomavirus-16 E7 and have found that this vaccine generates strong E7-specific antitumor immunity and antiangiogenic effects

Wen-Fang Cheng; Chien-Fu Hung; Chi-An Chen; Chien-Nan Lee; Yi-Ning Su; Chee-Yin Chai; David A. K. Boyd; Chang-Yao Hsieh; T.-C. Wu

2005-01-01

72

Transient Association of Calnexin and Calreticulin with Newly Synthesized G1 and G2 Glycoproteins of Uukuniemi Virus (Family Bunyaviridae)  

Microsoft Academic Search

The membrane glycoproteins G1 and G2 of Uukuniemi virus, a member of the Bunyaviridae family, are co- translationally cleaved from a common precursor in the endoplasmic reticulum (ER). Here, we show that newly made G1 and G2 associate transiently with calnexin and calreticulin, two lectins involved in glycoprotein fold- ing in the ER. Stable complexes between G1-G2 and calnexin or

JOHANNA VEIJOLA; RALF F. PETTERSSON

1999-01-01

73

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

PubMed Central

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

Allen, S; Bulleid, N J

1997-01-01

74

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

PubMed

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

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

2012-03-01

75

Epithelial calreticulin up-regulation promotes profibrotic responses and tubulointerstitial fibrosis development.  

PubMed

Renal fibrosis is the common anatomical feature underlying the progression of chronic kidney disease, a leading cause of morbidity and mortality worldwide. In a previous study, we demonstrated that during development of renal fibrosis in a rat model of unilateral ureteric obstruction, calreticulin (CRT) is up-regulated in tubular epithelial cells (TECs). In the present study, we used in vitro and in vivo approaches to examine the role of CRT in TECs and its contribution to the progression of fibrosis. In cultured renal TECs, CRT overexpression induced acquisition of an altered, profibrotic cellular phenotype. Consistently, the opposite effects were observed for CRT knockdown. Subsequently, we confirmed that critical changes observed in vitro were also apparent in tubular cells in vivo in the animal model of unilateral ureteric obstruction. In agreement with these results, we demonstrate that substantial (50%) reduction in the expression of CRT reduced the development of tubulointerstitial fibrosis at a comparable level through regulation of inflammation, transcriptional activation, transforming growth factor ?1-associated effects, and apoptosis. In summary, our findings establish that CRT is critically involved in the molecular mechanisms that drive renal fibrosis progression and indicate that inhibition of CRT expression might be a therapeutic target for reduction of fibrosis and chronic kidney disease development. PMID:24035512

Prakoura, Niki; Politis, Panagiotis K; Ihara, Yoshito; Michalak, Marek; Charonis, Aristidis S

2013-09-11

76

Self-Oligomerization Is Essential for Enhanced Immunological Activities of Soluble Recombinant Calreticulin  

PubMed Central

We have recently reported that calreticulin (CRT), a luminal resident protein, can be found in the sera of patients with rheumatoid arthritis and also that recombinant CRT (rCRT) exhibits extraordinarily strong immunological activities. We herein further demonstrate that rCRT fragments 18–412 (rCRT/18-412), rCRT/39-272, rCRT/120-308 and rCRT/120-250 can self-oligomerize in solution and are 50–100 fold more potent than native CRT (nCRT, isolated from mouse livers) in activating macrophages in vitro. We narrowed down the active site of CRT to residues 150–230, the activity of which also depends on dimerization. By contrast, rCRT/18-197 is almost completely inactive. When rCRT/18-412 is fractionated into oligomers and monomers by gel filtration, the oligomers maintain most of their immunological activities in terms of activating macrophages in vitro and inducing specific antibodies in vivo, while the monomers were much less active by comparison. Additionally, rCRT/18-412 oligomers are much better than monomers in binding to, and uptake by, macrophages. Inhibition of macrophage endocytosis partially blocks the stimulatory effect of rCRT/18-412. We conclude that the immunologically active site of CRT maps between residues 198–230 and that soluble CRT could acquire potent immuno-pathological activities in microenvironments favoring its oligomerization.

Huang, Shang-Hui; Zhao, Li-Xiang; Hong, Chao; Duo, Cui-Cui; Guo, Bing-Nan; Zhang, Li-Juan; Gong, Zheng; Xiong, Si-Dong; Gong, Fang-Yuan; Gao, Xiao-Ming

2013-01-01

77

Modulatory role of calreticulin as chaperokine for dendritic cell-based immunotherapy  

PubMed Central

Heat shock proteins (HSPs) play a regulatory role for maturation of antigen-presenting cells (APCs) such as dendritic cells (DCs) and macrophages. Whereas HSP70 has been shown to enhance the maturation of human DCs via a nuclear factor kappa-B (NF-?B)-dependent pathway, the regulatory role of calreticulin (CRT), which is a HSP with similar functions to HSP70, is not well studied. To investigate the role of CRT as adjuvant in cell activation and co-stimulatory responses we determined the effects of CRT on human APC maturation in comparison to that of HSP70. To facilitate eukaryotic endotoxin-free CRT protein expression, three different methods were compared. We demonstrate that CRT induces the maturation of human DCs and increases the production of proinflammatory cytokines via the NF-?B pathway. CRT-mediated maturation was qualitatively similar to that induced by HSP70. Interestingly, priming of monocytes with HSPs showed an even more prominent effect on maturation than exposure of immature DCs to these compounds. A higher expression of CD86, CD83 and CCR7 on mature DCs were found in response to CRT. Our data provide novel insights into the role of extracellular HSPs as chaperokines in the processes of APC generation and may thus be useful to improve adoptive immunotherapy.

Bajor, A; Tischer, S; Figueiredo, C; Wittmann, M; Immenschuh, S; Blasczyk, R; Eiz-Vesper, B

2011-01-01

78

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

PubMed Central

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

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

2012-01-01

79

Cloning and characterization of the calreticulin gene in Asian seabass (Lates calcarifer).  

PubMed

Calreticulin (CRT) is a Ca2+-binding molecular chaperone in the endoplasmic reticulum. We cloned and characterized the CRT gene in an important marine food fish species Asian seabass (Lates calcarifer). The full-length DNA of the CRT gene was 2194 bp, including a complete open reading frame encoding 420 amino acid residues, a 113 bp 5'-untranslated region and an 818 bp 3'-untranslated region. The CRT gene contained nine exons and eight introns covering a total of 2772 bp genomic DNA from the start to stop codon. Ten single nucleotide polymorphisms (SNPs) were detected in introns and an exon in six individuals collected from five different locations. The CRT gene was assigned to linkage group 4 of the linkage map of Asian seabass. Quantitative real-time PCR revealed that the CRT gene was highly expressed in liver at the age of 1, 3 and 7 months under normal conditions, whereas its expression in liver reduced sharply after 0.5 to 2 h cold challenge at 16°C, and then increased slowly. A preliminary association analysis showed a significant (P < 0.001) association between the SNP6 in the CRT gene and the mortality after cold challenge at 16°C. Our results suggest that the CRT gene is associated with cold tolerance of Asian seabass and further investigation will be necessary to illustrate the underlying mechanisms. PMID:22558958

Bai, Z Y; Zhu, Z Y; Wang, C M; Xia, J H; He, X P; Yue, G H

2012-06-01

80

Mechanisms of pre-apoptotic calreticulin exposure in immunogenic cell death  

PubMed Central

Dying tumour cells can elicit a potent anticancer immune response by exposing the calreticulin (CRT)/ERp57 complex on the cell surface before the cells manifest any signs of apoptosis. Here, we enumerate elements of the pathway that mediates pre-apoptotic CRT/ERp57 exposure in response to several immunogenic anticancer agents. Early activation of the endoplasmic reticulum (ER)-sessile kinase PERK leads to phosphorylation of the translation initiation factor eIF2?, followed by partial activation of caspase-8 (but not caspase-3), caspase-8-mediated cleavage of the ER protein BAP31 and conformational activation of Bax and Bak. Finally, a pool of CRT that has transited the Golgi apparatus is secreted by SNARE-dependent exocytosis. Knock-in mutation of eIF2? (to make it non-phosphorylatable) or BAP31 (to render it uncleavable), depletion of PERK, caspase-8, BAP31, Bax, Bak or SNAREs abolished CRT/ERp57 exposure induced by anthracyclines, oxaliplatin and ultraviolet C light. Depletion of PERK, caspase-8 or SNAREs had no effect on cell death induced by anthracyclines, yet abolished the immunogenicity of cell death, which could be restored by absorbing recombinant CRT to the cell surface.

Panaretakis, Theocharis; Kepp, Oliver; Brockmeier, Ulf; Tesniere, Antoine; Bjorklund, Ann-Charlotte; Chapman, Daniel C; Durchschlag, Michael; Joza, Nicholas; Pierron, Gerard; van Endert, Peter; Yuan, Junying; Zitvogel, Laurence; Madeo, Frank; Williams, David B; Kroemer, Guido

2009-01-01

81

PTP1B Contributes to Calreticulin-Induced Metastatic Phenotypes in Esophageal Squamous Cell Carcinoma.  

PubMed

Calreticulin (CRT) is a Ca(2+)-binding chaperone protein that alters cellular Ca(2+)-homeostasis in the endoplasmic reticulum (ER). Previously it was shown that CRT was overexpressed in esophageal squamous cell carcinoma (ESCC), and elevated CRT expression promoted the migration and invasion of ESCC cells. In the present study, the mechanisms underlying the role of CRT in esophageal carcinoma progression were investigated. Critically, depletion of CRT or protein-tyrosine phosphatase 1B (PTP1B) reduced ESCC cell migration and metastasis to the lung, whereas restoration of PTP1B protein levels rescued cell migration in CRT-silenced cells. Knockdown of CRT decreased PTP1B protein expression by reducing phosphorylation at the Y694 site of STAT5A, whereas knockdown of PTP1B reduced ERK1/2 phosphorylation at T204. Immunohistochemical analysis of CRT and PTP1B expression in ESCC patient tissues was strongly correlated. Importantly, PTP1B expression was associated with poor survival in patients with CRT overexpression. Overall, these data indicate a novel signaling pathway connecting CRT, STAT5A, PTP1B, and ERK1/2 in the regulation of ESCC cell migration. Implications: These findings suggest that PTP1B is a downstream effector of CRT signaling, promotes tumor progression, and can potentially be used as a new drug target for ESCC. Mol Cancer Res; 11(9); 986-94. ©2013 AACR. PMID:23814025

Wang, Xiao-Min; Shang, Li; Zhang, Yu; Hao, Jia-Jie; Shi, Feng; Luo, Wei; Zhang, Tong-Tong; Wang, Bo-Shi; Yang, Yang; Liu, Zhi-Hua; Zhan, Qi-Min; Wang, Ming-Rong

2013-06-27

82

Self-oligomerization is essential for enhanced immunological activities of soluble recombinant calreticulin.  

PubMed

We have recently reported that calreticulin (CRT), a luminal resident protein, can be found in the sera of patients with rheumatoid arthritis and also that recombinant CRT (rCRT) exhibits extraordinarily strong immunological activities. We herein further demonstrate that rCRT fragments 18-412 (rCRT/18-412), rCRT/39-272, rCRT/120-308 and rCRT/120-250 can self-oligomerize in solution and are 50-100 fold more potent than native CRT (nCRT, isolated from mouse livers) in activating macrophages in vitro. We narrowed down the active site of CRT to residues 150-230, the activity of which also depends on dimerization. By contrast, rCRT/18-197 is almost completely inactive. When rCRT/18-412 is fractionated into oligomers and monomers by gel filtration, the oligomers maintain most of their immunological activities in terms of activating macrophages in vitro and inducing specific antibodies in vivo, while the monomers were much less active by comparison. Additionally, rCRT/18-412 oligomers are much better than monomers in binding to, and uptake by, macrophages. Inhibition of macrophage endocytosis partially blocks the stimulatory effect of rCRT/18-412. We conclude that the immunologically active site of CRT maps between residues 198-230 and that soluble CRT could acquire potent immuno-pathological activities in microenvironments favoring its oligomerization. PMID:23762269

Huang, Shang-Hui; Zhao, Li-Xiang; Hong, Chao; Duo, Cui-Cui; Guo, Bing-Nan; Zhang, Li-Juan; Gong, Zheng; Xiong, Si-Dong; Gong, Fang-Yuan; Gao, Xiao-Ming

2013-06-10

83

Molecular cloning and characterization of sea bass (Dicentrarchus labrax, L.) calreticulin.  

PubMed

Mammalian calreticulin (CRT) is a key molecular chaperone and regulator of Ca(2+) homeostasis in endoplasmic reticulum (ER), also being implicated in a variety of physiological/pathological processes outside the ER. Importantly, it is involved in assembly of MHC class I molecules. In this work, sea bass (Dicentrarchus labrax) CRT (Dila-CRT) gene and cDNA have been isolated and characterized. The mature protein retains two conserved motifs, three structural/functional domains (N, P and C), three type 1 and 2 motifs repeated in tandem, a conserved pair of cysteines and ER-retention motif. It is a single-copy gene composed of 9 exons. Dila-CRT three-dimensional homology models are consistent with the structural features described for mammalian molecules. Together, these results are supportive of a highly conserved structure of CRT through evolution. Moreover, the present data provides information that will allow further studies on sea bass CRT involvement in immunity and in particular class I antigen presentation. PMID:23523749

Pinto, Rute D; Moreira, Ana R; Pereira, Pedro J B; dos Santos, Nuno M S

2013-03-22

84

A Sandwich Enzyme-linked Immunosorbent Assay for Detection of Calreticulin in Human Serum.  

PubMed

Calreticulin (CRT) is a 46?kDa Ca(2+) binding chaperone protein that is mainly located in the endoplasmic reticulum luminal and has various biological functions. It is important to establish a specific and sensitive CRT enzyme-linked immunosorbent assay (ELISA) for the study of CRT functions. Therefore, we prepared a polyclonal antibody (PAb) in rabbits immunized with a recombinant CRT protein. Based on the PAb and our previously prepared monoclonal antibody (MAb), a highly specific and sensitive ELISA was developed. In the present study, we describe a sandwich ELISA for the determination of CRT protein in human serum. It was found that soluble CRT (sCRT) concentration in serum samples from 49 lung cancer patients was significantly higher than that from 53 healthy individuals (p=0.004). This result demonstrates that sCRT concentration in sera of lung cancer patients is higher than that in sera of healthy individuals. In conclusion, the prepared CRT antibodies and developed ELISA is a potential tool for CRT research and offers an alternative, simple, rapid technique for detecting CRT, especially in large ongoing and future clinical studies. PMID:24111870

Wu, Wei; Wang, Gongze; Tan, Chao; Zou, Xiaohua; Wang, Yanlin; Liu, Chaoqi

2013-10-01

85

Thrombospondin-1 Interacts with Trypanosoma cruzi Surface Calreticulin to Enhance Cellular Infection  

PubMed Central

Trypanosoma cruzi causes Chagas disease, which is a neglected tropical disease that produces severe pathology and mortality. The mechanisms by which the parasite invades cells are not well elucidated. We recently reported that T. cruzi up-regulates the expression of thrombospondin-1 (TSP-1) to enhance the process of cellular invasion. Here we characterize a novel TSP-1 interaction with T. cruzi that enhances cellular infection. We show that labeled TSP-1 interacts specifically with the surface of T. cruzi trypomastigotes. We used TSP-1 to pull down interacting parasite surface proteins that were identified by mass spectrometry. We also show that full length TSP-1 and the N-terminal domain of TSP-1 (NTSP) interact with T. cruzi surface calreticulin (TcCRT) and other surface proteins. Pre-exposure of recombinant NTSP or TSP-1 to T. cruzi significantly enhances cellular infection of wild type mouse embryo fibroblasts (MEF) compared to the C-terminal domain of TSP-1, E3T3C1. In addition, blocking TcCRT with antibodies significantly inhibits the enhancement of cellular infection mediated by the TcCRT-TSP-1 interaction. Taken together, our findings indicate that TSP-1 interacts with TcCRT on the surface of T. cruzi through the NTSP domain and that this interaction enhances cellular infection. Thus surface TcCRT is a virulent factor that enhances the pathogenesis of T. cruzi infection through TSP-1, which is up-regulated by the parasite.

Johnson, Candice A.; Kleshchenko, Yulia Y.; Ikejiani, Adaeze O.; Udoko, Aniekanabasi N.; Cardenas, Tatiana C.; Pratap, Siddharth; Duquette, Mark A.; Lima, Maria F.; Lawler, Jack; Villalta, Fernando; Nde, Pius N.

2012-01-01

86

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

PubMed Central

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

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

2007-01-01

87

Lysyl tRNA synthetase is required for the translocation of calreticulin to the cell surface in immunogenic death.  

PubMed

In response to immunogenic cell death inducers, calreticulin (CRT) translocates from its orthotopic localization in the lumen of the endoplasmic reticulum (ER) to the surface of the plasma membrane where it serves as an engulfment signal for antigen-presenting cells.(1) Here, we report that yet another ER protein, the lysyl-tRNA synthetase (KARS), was exposed on the surface of stressed cells, on which KARS co-localized with CRT in lipid rafts. Depletion of KARS with small interfering RNAs suppressed CRT exposure induced by anthracyclines or UVC light. In contrast to CRT, KARS was also found in the supernatant of stressed cells. Recombinant KARS protein was unable to influence the binding of recombinant CRT to the cell surface. Moreover, recombinant KARS protein was unable to stimulate macrophages in vitro. These results underscore the contribution of KARS to the emission of (one of) the principal signal(s) of immunogenic cell death, CRT exposure. PMID:20699648

Kepp, Oliver; Gdoura, Abdelaziz; Martins, Isabelle; Panaretakis, Theocharis; Schlemmer, Frederic; Tesniere, Antoine; Fimia, Gian Maria; Ciccosanti, Fabiola; Burgevin, Anne; Piacentini, Mauro; Eggleton, Paul; Young, Philip J; Zitvogel, Laurence; van Endert, Peter; Kroemer, Guido

2010-08-23

88

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

PubMed Central

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

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

1994-01-01

89

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

PubMed

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

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

1994-09-01

90

Catalyzed Ceramic Burner Material  

SciTech Connect

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

Barnes, Amy S., Dr.

2012-06-29

91

Potassium Phosphate Catalyzed Nitroaldol Reaction  

Microsoft Academic Search

Potassium phosphate was found to catalyze condensation of nitroalkanes with various aliphatic and aromatic aldehydes to form nitroaldols in excellent yields in acetonitrile medium at room temperature.

Uday V. Desai; D. M. Pore; R. B. Mane; S. B. Solabannavar; P. P. Wadgaonkar

2004-01-01

92

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

PubMed Central

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

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

1997-01-01

93

Immunological mechanisms involved in the protection against intestinal taeniosis elicited by oral immunization with Taenia solium calreticulin.  

PubMed

Oral immunization with functional recombinant Taenia solium calreticulin (rTsCRT) induces 37% reduction in tapeworm burden in the experimental model of intestinal taeniosis in hamsters. Furthermore, tapeworms recovered from vaccinated animals exhibit diminished length, being frequently found in more posterior parts of the small intestine. The aim of this study was to analyze the immunological mechanisms involved in protection in response to rTsCRT oral immunization. Hamsters were orally immunized with rTsCRT using cholera toxin (CT) as adjuvant, weekly for 4 weeks. Fifteen days after the last boost animals were challenged with four T. solium cysticerci. Reduction in the adult worm recovery and increased transcription of mRNA for IL-4 and IFN-? in the mucosa of rTsCRT+CT immunized animals were observed. Immunization also induced goblet cell hyperplasia in the mucosa surrounding the implantation site of the parasite. Specific IgG and IgA antibodies in serum and fecal supernatants were detected after the second immunization, being more pronounced after challenge. Our data suggest that oral vaccination with rTsCRT+CT regulates a local expression of IL-4 and IFN-?, stimulating secretion of IgA that, together with the increase of goblet cells and mucin production, could result in an unfavorable environment for T. solium promoting an impaired tapeworm development. PMID:22921496

Leon-Cabrera, Sonia; Cruz-Rivera, Mayra; Mendlovic, Fela; Romero-Valdovinos, Mirza; Vaughan, Gilberto; Salazar, Ana María; Avila, Guillermina; Flisser, Ana

2012-08-16

94

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

PubMed

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

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

2013-05-24

95

Investigations on the C1q-calreticulin-phosphatidylserine interactions yield new insights into apoptotic cell recognition.  

PubMed

Both C1q and calreticulin (CRT) are involved in the recognition of apoptotic cells. CRT was initially characterized as a receptor for the C1q collagen-like fragment (CLF), whereas C1q was shown to bind apoptotic cells through its globular region (GR). Using purified CRT and recombinant CRT domains, we now provide unambiguous experimental evidence that, in addition to its CLF, the C1q GR also binds CRT and that both types of interactions are mediated by the CRT globular domain. Surface plasmon resonance analyses revealed that the C1q CLF and GR domains each bind individually to immobilized CRT and its globular domain with K(D) values of (2.6-8.3) × 10(-7) M. Further evidence that CRT binds to the C1q GR was obtained by electron microscopy. The role of CRT in the recognition of apoptotic HeLa cells by C1q was analyzed. The C1q GR partially colocalized with CRT on the surface of early apoptotic cells, and siRNA (small interfering RNA)-induced CRT deficiency resulted in increased apoptotic cell binding to C1q. The interaction between CRT and phosphatidylserine (PS), a known C1q ligand on apoptotic cells, was also investigated. The polar head of PS was shown to bind to CRT with a 10-fold higher affinity (K(D)=1.5 × 10(-5) M) than that determined for C1q, and, accordingly, the C1q GR-PS interaction was impaired in the presence of CRT. Together, these observations indicate that CRT, C1q, and PS are all closely involved in the uptake of apoptotic cells and strongly suggest a combinatorial role of these three molecules in the recognition step. PMID:21352829

Païdassi, Helena; Tacnet-Delorme, Pascale; Verneret, Mélanie; Gaboriaud, Christine; Houen, Gunnar; Duus, Karen; Ling, Wai Li; Arlaud, Gérard J; Frachet, Philippe

2011-02-23

96

Functional cooperation between BiP and calreticulin in the folding maturation of a glycoprotein in Trypanosoma cruzi  

PubMed Central

Proteins may adopt diverse conformations during their folding in vivo, ranging from extended chains when they emerge from the ribosome to compact intermediates near the end of the folding process. Accordingly, a variety of chaperones and folding assisting enzymes have evolved to deal with this diversity. Chaperone selection by a particular substrate depends on the structural features of its folding intermediates. In addition, this process may be modulated by competitive effects between chaperones. Here we address this issue by using TcrCATL as model substrate. TcrCATL is an abundant Trypanosoma cruzi lysosomal protease and it was the first identified endogenous UDP-Glc:glycoprotein glucosyltransferase (UGGT) substrate. We found that TcrCATL associated sequentially with BiP and calreticulin (CRT) during its folding process. Early, extended conformations were bound to BiP, while more advanced and compact folding intermediates associated to CRT. The interaction between TcrCATL and CRT was impeded by deletion of the UGGT-encoding gene but, similarly to what was observed in wild type cells, in mutant cells TcrCATL associated to BiP only when displaying extended conformations. The absence of TcrCATL–CRT interactions in UGGT null cells resulted in a drastic reduction of TcrCATL folding efficiency and triggered the aggregation of TcrCATL through intermolecular disulfide bonds. These observations show that BiP and CRT activities complement each other to supervise a complete and efficient TcrCATL folding process. The present report provides further evidence on the early evolutionary acquisition of the basic tenets of the N-glycan dependent quality control mechanism of glycoprotein folding.

Labriola, Carlos A.; Villamil Giraldo, Ana M.; Parodi, Armando J.; Caramelo, Julio J.

2011-01-01

97

Bruton's tyrosine kinase is required for apoptotic cell uptake via regulating the phosphorylation and localization of calreticulin.  

PubMed

In addition to regulating B cell development and activation, Bruton's tyrosine kinase (Btk) functions downstream of multiple TLRs, including TLR7, to regulate innate immune responses in myeloid cells. Although critical for defense against RNA viruses such as influenza and Sendai virus, recognition of self-RNA by TLR7 also has been shown to be an important contributor to the pathophysiology of systemic lupus erythematosus. To date, the role of Btk in regulating TLR7-mediated responses is poorly understood. In the current study, we have demonstrated a hitherto undiscovered role for Btk in apoptotic cell uptake, identifying the molecular chaperone calreticulin (CRT) as a novel substrate for Btk in regulating this response. CRT together with the transmembrane receptor CD91 function at the cell membrane and regulate uptake of C1q-opsonised apoptotic cells. Our results show that Btk directly phosphorylates CRT and that in the absence of Btk, CRT fails to localize with CD91 at the cell surface and at the phagocytic cup. Critically, a blocking Ab against CRT in wild-type macrophages mimics the inability of Btk-deficient macrophages to phagocytose apoptotic cells efficiently, indicating the critical importance of Btk in regulating CRT-driven apoptotic cell uptake. Our data have revealed a novel regulatory role for Btk in mediating apoptotic cell clearance, with CRT identified as the critical component of the CRT/CD91/C1q system targeted by Btk. Given the importance of clearing apoptotic cell debris to prevent inappropriate exposure of TLRs to endogenous ligands, our results have important implications regarding the role of Btk in myeloid cell function. PMID:23596312

Byrne, Jennifer C; Ní Gabhann, Joan; Stacey, Kevin B; Coffey, Barbara M; McCarthy, Eoghan; Thomas, Warren; Jefferies, Caroline A

2013-04-17

98

Recombined DNA vaccines encoding calreticulin linked to HPV6bE7 enhance immune response and inhibit angiogenic activity in B16 melanoma mouse model expressing HPV 6bE7 antigen  

Microsoft Academic Search

Calreticulin (CRT) has been reported to have an effect of upregulating MHC class I presentation as well as inhibiting angiogenesis in vitro and in vivo. Combination of dual mechanisms of enhanced immunogenicity of human papillomavirus (HPV) 6bE7 antigen and antiangiogenesis may be introduced in the strategy of vaccines against condyloma acuminatum (CA) resulting from HPV infection. Therefore, we constructed DNA

Ke-Jia Zhao; Hao Cheng; Ke-Jian Zhu; Yan Xu; Min-li Chen; Xing Zhang; Tao Song; Jun Ye; Qi Wang; Da-Fang Chen

2006-01-01

99

Homogeneous Copper-Catalyzed Oxidations  

Microsoft Academic Search

The bioinorganic chemistry of copper has provided a stimulating background for exciting research\\u000a on homogeneous copper-catalyzed reactions in recent years, and this review starts with a brief and\\u000a concise overview of the role of copper containing active sites in metalloproteins that catalyze oxidation\\u000a or oxygenation reactions in nature. Efficient bio-inspired Cu-based catalysts for a variety of chemical\\u000a oxidative transformations have been developed over

Jarl Ivar van der Vlugt; Franc Meyer

100

Compressibility of cold catalyzed matter  

Microsoft Academic Search

The properties of cold catalyzed matter (CCM) of density near and above the density characteristic of the central region of heavy atomic nuclei are of fundamental importance for the physics of neutron stars. In this paper the compression modulus of CCM (an electrically neutral, spatially homogeneous mixture of electrons, neutrons, and protons at a temperature of 0 K) is studied

P. Haensel

1980-01-01

101

Chloroperoxidase-Catalyzed Benzylic Hydroxylation  

Microsoft Academic Search

Chloroperoxidase oxidizes p-methylanisole and p-ethylanisole to 4-methoxybenzyl alcohol and 1-(4?-methoxyphenyl)ethanol, respectively. It ineffectively oxidizes toluene to benzyl alcohol but does not appear to oxidize toluene substituted with strong electron-withdrawing groups. O-Demethylation is also observed. The enzyme is sensitive to substituents at other than the para position and does not detectably catalyze benzylic hydroxylation of p-methylanisole if it bears additional methyl

V. P. Miller; R. A. Tschirretguth; P. R. O. Demontellano

1995-01-01

102

Selective Oxidations Catalyzed by Chloroperoxidase (Selectieve Oxidaties Gekatalyseerd door Chloorperoxidase).  

National Technical Information Service (NTIS)

Content: Introduction; Selective oxidations catalyzed by peroxidases; Chloroperoxidase catalyzed sulfoxidations in tert-butyl alcohol/water mixtures; Synthesis of substituted oxindoles by chloroperoxidase catalyzed oxidation of indoles; Chloroperoxidase c...

M. P. J. van Deurzen

1996-01-01

103

Muon-catalyzed fusion theory  

SciTech Connect

Some topics in muon-catalyzed fusion theory are discussed: Resonant formation of dd{mu} molecules appears to be well understood, with good agreement so far between theory and experiment. The situation for resonant dt{mu} formation is much less clear, because of the more complicated kinetics, the apparent three-body effect, and the evident need to treat thermalization and molecular formation together to compare theory and experiment. Recent theoretical progress in pd{mu} fusion by Friar et al. has resolved a serious discrepancy in the Wolfenstein-Gershtein effect, i.e., the increase in pd{mu} fusion yield with increased deuterium fraction. 44 refs., 8 figs., 2 tabs.

Leon, M.

1991-01-01

104

Additive effect of calreticulin and translation initiation factor eIF4E on secreted protein production in the baculovirus expression system.  

PubMed

The baculovirus expression vector system is widely used for the production of recombinant proteins. However, the yield of membrane-bound or secreted proteins is relatively low when compared with intracellular or nuclear proteins. In a previous study, we had demonstrated that the co-expression of the human chaperones calreticulin (CALR) or ?-synuclein (?-syn) increased the production of a secreted protein considerably. A similar effect was also seen when co-expressing insect translation initiation factor eIF4E. In this study, different combinations of the three genes were tested (CALR alone, ?-syn?+?CALR, or ?-syn?+?CALR?+?eIF4E) to further improve secretory protein production by assessing the expression level of a recombinant secreted alkaline phosphatase (SEFP). An additional 1.8-fold increment of SEFP production was obtained when cells co-expressed all the three "helper" genes, compared to cells, in which only CALR was co-produced with SEFP. Moreover, the duration of the SEFP production lasted much longer in cells that co-expressed these three "helper" genes, up to 10 dpi was observed. Utilization of this "triple-supporters" containing vector offers significant advantages when producing secreted proteins and is likely to have benefits for the production of viral vaccines and other pharmaceutical products. PMID:23900798

Teng, Chao-Yi; van Oers, Monique M; Wu, Tzong-Yuan

2013-07-31

105

Effect of calreticulin on Ca2+/CaM kinaseII? and endoplasmic reticulum stress in hippocampal in a rat model of post-traumatic stress disorder.  

PubMed

The purpose of the present study was to examine the changes in the molecular chaperone calreticulin (CRT), calcium signaling pathway Ca(2+)-calmodulin (CaM)-CaM kinaseII? (CaMKII?), and the endoplasmic reticulum (ER) apoptotic modulator caspase-12 in hippocampal neurons of rats exposed to single-prolonged stress (SPS), a model of post-traumatic stress disorder (PTSD). Molecular markers and proteins were assessed using immunohistochemistry, western blot and reverse transcript-polymerase chain reaction in rats exposed to SPS at 1 day (1d), 4 and 7 days post-stress and time matched controls. We found that at 7 days, SPS rats had the highest CRT expression. The intracellular free Ca(2+) and the CaM expression reached peak at 1 day post-SPS whereas the CaMKII? had the opposite trend. Caspase-12 was most active at 4 days and was found to decrease thereafter. Signs of apoptosis were identified using transmission electron microscopy in the rats exposed to SPS. The results indicate that signs of ER stress in the hippocampus of rats exposed to SPS trigger the molecular changes in the intracellular cytoplasm which in turn activate the apoptotic pathway through caspase-12. Therefore, we propose that the hippocampal apoptosis could be one of the pathological mechanisms related to the memory disorders in PTSD. PMID:23575574

Liu, Hong; Han, Fang; Shi, Yuxiu

2013-04-11

106

Enhanced protein secretion from insect cells by co-expression of the chaperone calreticulin and translation initiation factor eIF4E.  

PubMed

Host protein synthesis is shut down in the lytic baculovirus expression vector system (BEVS). This also affects host proteins involved in routing secretory proteins through the endoplasmic reticulum (ER)-Golgi system. It has been demonstrated that a secretory alkaline phosphatase-EGFP fusion protein (SEFP) can act as a traceable and sensitive secretory reporter protein in BEVS. In this study, a chaperone, calreticulin (CALR), and the translation initiation factor eIF4E were co-expressed with SEFP using a bicistronic baculovirus expression vector. We observed that the intracellular distribution of SEFP in cells co-expressing CALR was different from co-expressing eIF4E. The increased green fluorescence emitted by cells co-expressing CALR had a good correlation with the abundance of intracellular SEFP protein and an unconventional ER expansion. Cells co-expressing eIF4E, on the other hand, showed an increase in extracellular SEAP activity compared to the control. Utilization of these baculovirus expression constructs containing either eIF4E or CALR offers a significant advantage for producing secreted proteins for various biotechnological and therapeutic applications. PMID:22555850

Teng, Chao-Yi; Chang, Shou-Lin; van Oers, Monique M; Wu, Tzong-Yuan

2013-05-01

107

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

PubMed Central

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

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

2013-01-01

108

Calreticulin functions as a molecular chaperone for the ?-amyloid precursor protein 1 1 Abbreviations used: A?, ?-amyloid peptide; AD, Alzheimer’s disease; APP, ?-amyloid precursor protein; CHAPS, 3-[(3-Cholamidopropyl)-dimethylammonio]-1-propanesulfonate; Crt, calreticulin; DMEM, Dulbecco’s Modified Eagle Medium; DMJ, deoxymannojirimycin; DTSSP, 3,3?Dithio bis (sulfosuccinimidylpropionate); ECL, Enhanced Chemiluminescence; ER, endoplasmic reticulum; FBS, fetal bovine serum; HRP, horseradish peroxidase; kDa, kiloDaltons; MES, 2-(N-Morpholino) ethane sulfonic acid; NRS, normal rabbit serum; PBS, PBS; PMSF, phenymethylsulfonyl fluoride; PVDF, polyvinylidene fluoride  

Microsoft Academic Search

Processing of the ?-amyloid precursor protein (APP) in the endoplasmic reticulum and the Golgi apparatus may be critical in generating the ?-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

Robin J. Johnson; Guangqing Xiao; Janani Shanmugaratnam; Richard E. Fine

2001-01-01

109

Thermodynamics of reactions catalyzed by PABA synthase  

Microsoft Academic Search

Microcalorimetry and high-performance liquid chromatography (HPLC) have been used to conduct a thermodynamic investigation of reactions catalyzed by PABA synthase, the enzyme located at the first step in the shikimic acid metabolic pathway leading from chorismate to 4-aminobenzoate (PABA). The overall biochemical reaction catalyzed by the PabB and PabC components of PABA synthase is: chorismate(aq)+ammonia(aq)=4-aminobenzoate(aq)+pyruvate(aq)+H2O(l). This reaction can be divided

Yadu B. Tewari; Pia Y. Jensen; Nand Kishore; Martin P. Mayhew; James F. Parsons; Edward Eisenstein; Robert N. Goldberg

2002-01-01

110

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

PubMed

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

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

2013-08-01

111

Zeolite 5A Catalyzed Etherification of Diphenylmethanol  

ERIC Educational Resources Information Center

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

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

2009-01-01

112

Cobalt-catalyzed cross-coupling reactions  

Microsoft Academic Search

In the last few years, we and other groups have demonstrated that economical cobalt salts can advantageously replace expensive and toxic catalysts for cross coupling reactions. These cobalt- catalyzed reactions have considerably extended the range of functionalized compounds. A variety of sensitive functional groups can be tolerated in these coupling reactions and various organic compounds RX could be involved (R

Corinne Gosmini; Jeanne-Marie Begouin; Aurélien Moncomble

2008-01-01

113

Vanadium-catalyzed deoxydehydration of glycols.  

PubMed

A survey of several metavandate (VO3(-)) and chelated dioxovanadium derivatives shows that tetrabutylammonium dioxovanadium(v)dipicolinate most effectively catalyzes the deoxydehydration (DODH) of glycols to olefins in moderate to excellent yields with triphenylphosphine or sodium sulfite as reductants. PMID:23925040

Chapman, Garry; Nicholas, Kenneth M

2013-08-20

114

Urea-catalyzed construction of oxazinanes.  

PubMed

Highly functionalized oxazinanes are efficiently prepared through urea-catalyzed formal [3 + 3] cycloaddition reactions of nitrones and nitrocyclopropane carboxylates. The reaction system is general with respect to both the nitrocyclopropane carboxylates and nitrones enabling the preparation of a large family of oxazinanes, typically in high yield. This method affords access to enantioenriched oxazinane products through chirality transfer from enantioenriched nitrocyclopropane carboxylates. PMID:23907178

Hardman, Andrea M; So, Sonia S; Mattson, Anita E

2013-08-14

115

Direct conversion of muon catalyzed fusion energy.  

National Technical Information Service (NTIS)

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

T. Tajima S. Eliezer R. M. Kulsrud

1990-01-01

116

Antibody-Catalyzed Degradation of Cocaine  

Microsoft Academic Search

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

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

1993-01-01

117

Lipase-catalyzed synthesis of partial glyceride  

Microsoft Academic Search

Mucor miehei (IM 20) and Candida antarctica (SP 382) lipases were used for esterification of free fatty acids in the absence of organic solvent or transesterification of fatty acid methyl esters in hexane with isopropylidene glycerols. Acid catalyzed cleavage of the isopropylidene groups resulted in the formation of monoacyl glycerol (MAG) and diacyl glycerol (DAG). Both oleic (18:1 n-9) and

Casimir C. Akoh

1993-01-01

118

Ceramic forming using enzyme catalyzed reactions  

Microsoft Academic Search

A new colloidal processing method for near net shaping ceramic components is outlined. The Direct Coagulation Casting (DCC) process offers the opportunity to produce complex shaped components of high mechanical strength and high reliability at low costs.The process relies on electrostatic stabilized ceramic suspensions and it’s destabilization by time delayed in situ reactions. Enzyme catalyzed reactions may be used either

L. J. Gauckler; Th. Graule; F. Baader

1999-01-01

119

Ruthenium-Catalyzed Synthesis of Heterocyclic Compounds  

Microsoft Academic Search

Heterocyclic compounds have been synthesized by means of stoichiometric reagents under acidic or basic conditions. Recent progress of homogeneous transition-metal catalysis realizes a highly selective and atom-economical methodology for synthesis of heterocycles under neutral and mild conditions. This review highlights the recent advances in the area of ruthenium-catalyzed syntheses of heterocyclic compounds.

Yoshihiko Yamamoto; Kenji Itoh

120

Homogeneous pd-catalyzed enantioselective decarboxylative protonation.  

PubMed

General homogeneous conditions for the palladium-catalyzed synthesis of carbonyl compounds with tertiary carbon stereocenters at the alpha-position are reported. The highly reactive catalyst tolerates a variety of substrate substitution and functionality, and generates enantioenriched cyclic ketones from racemic allyl beta-ketoester starting materials. PMID:18303896

Marinescu, Smaranda C; Nishimata, Toyoki; Mohr, Justin T; Stoltz, Brian M

2008-02-28

121

Heterogeneously-Catalyzed Conversion of Carbohydrates  

NASA Astrophysics Data System (ADS)

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

Vigier, Karine De Oliveira; Jérôme, François

122

Palladium-catalyzed amination of aryl nonaflates.  

PubMed

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

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

2003-12-12

123

Fusion characteristics in exotic catalyzed systems  

SciTech Connect

Muon catalyzed fusion represents a potential long-term approach to fusion power. The sensitivity of the fusion properties of muomolecules to the choice of wave function describing the system is studied. The need for an improved understanding of the problem and correct evaluation of nonadiabatic effects is stressed, and the discrepancy between fusion rates from Born-Oppenheimer- and Hylleraas-type wave functions is pointed out.

Chatterjee, L.; Gautam, V.P.

1985-05-01

124

Iron-catalyzed asymmetric haloamination reactions.  

PubMed

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

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

2013-08-01

125

Silver-Catalyzed Late-Stage Fluorination  

PubMed Central

Carbon–fluorine bond formation by transition metal catalysis is difficult and only few methods for the synthesis of aryl fluorides have been developed. All reported transition metal-catalyzed fluorination reactions for the synthesis of functionalized arenes are based on palladium. Here we present silver catalysis for carbon–fluorine bond formation. Our report is the first example of the use of the transition metal silver to form carbon–heteroatom bonds by cross-coupling catalysis. The functional group tolerance and substrate scope presented here have not been demonstrated for any other fluorination reaction to date.

Tang, Pingping; Furuya, Takeru

2010-01-01

126

Gold-catalyzed synthesis of iodofulvenes.  

PubMed

We report the gold-catalyzed synthesis of highly functionalized iodofulvenes from iododialkynes under mild conditions. The catalytic cycle involves the formation of gold acetylides and vinylgold intermediates. These intermediates can then undergo an unprecedented iodine/gold exchange. This new pathway for catalyst transfer in dual gold catalysis opens up the possibility of highly regioselective transformations directed by the gold in the organogold intermediates. The resulting products are well suited for further metal-mediated coupling reactions, allowing the synthesis of extended ?-systems. PMID:23653259

Nösel, Pascal; Lauterbach, Tobias; Rudolph, Matthias; Rominger, Frank; Hashmi, A Stephen K

2013-05-07

127

Nitroreductase catalyzed biotransformation of CL20  

Microsoft Academic Search

Previously, we reported that a salicylate 1-monooxygenase from Pseudomonas sp. ATCC 29352 biotransformed CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane) (C6H6N12O12) and produced a key metabolite with mol. wt. 346Da corresponding to an empirical formula of C6H6N10O8 which spontaneously decomposed in aqueous medium to produce N2O, NH4+, and HCOOH [Appl. Environ. Microbiol. (2004)]. In the present study, we found that nitroreductase from Escherichia coli catalyzed

Bharat Bhushan; Annamaria Halasz; Jalal Hawari

2004-01-01

128

N-Heterocyclic Carbene-Catalyzed Oxidations  

PubMed Central

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

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

2009-01-01

129

Highly chemoselective calcium-catalyzed propargylic deoxygenation.  

PubMed

A calcium-catalyzed direct reduction of propargylic alcohols and ethers has been accomplished by using triethylsilane as a nucleophilic hydride source. At room temperature a variety of secondary propargylic alcohols was deoxygenated to the corresponding hydrocarbons in excellent yields. Furthermore, for the first time, a catalytic deoxygenation of tertiary propargylic alcohols was generally applicable. The same protocol was suitable for an efficient reduction of secondary as well as tertiary propargylic methyl, benzyl and allyl ethers. Substrates containing an additional keto-, ester or secondary hydroxyl function were reduced with exceptional chemoselectivity at the propargylic position. PMID:22378484

Meyer, Vera J; Niggemann, Meike

2012-02-29

130

Biginelli Reaction Catalyzed by Copper Nanoparticles  

PubMed Central

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

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

2012-01-01

131

Mechanism of combustion of catalyzed double base propellants  

Microsoft Academic Search

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

H. Singh; K. R. K. Rao

1988-01-01

132

Titanium-catalyzed C-F activation of fluoroalkenes.  

PubMed

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

Kühnel, Moritz F; Lentz, Dieter

2010-03-12

133

Acid-Catalyzed Isomerization of Carvone to Carvacrol  

ERIC Educational Resources Information Center

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

Kjonaas, Richard A.; Mattingly, Shawn P.

2005-01-01

134

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...

135

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

PubMed Central

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

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

2011-01-01

136

Synthetic applications of gold-catalyzed ring expansions  

PubMed Central

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

Garayalde, David

2011-01-01

137

Acid-Catalyzed Isomerization of Carvone to Carvacrol  

ERIC Educational Resources Information Center

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

Kjonaas, Richard A.; Mattingly, Shawn P.

2005-01-01

138

Representing Rate Equations for Enzyme-Catalyzed Reactions  

ERIC Educational Resources Information Center

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

Ault, Addison

2011-01-01

139

Palladium-catalyzed asymmetric benzylation of azlactones.  

PubMed

Asymmetric benzylation of prochiral azlactone nucleophiles enables the catalytic introduction of a benzyl group towards the synthesis of ?,?-disubstituted amino acids. Herein, we report an enantioselective palladium-catalyzed process using chiral bis(diphenylphosphinobenzoyl)diamine (dppba) ligands. Naphthalene- and heterocycle-based methyl carbonates react with a number of azlactones derived from both natural and unnatural amino acids. Monocyclic benzylic electrophiles, for which the barrier to ionization is higher, must employ a phosphate leaving group in order to react. Reaction conditions for electron-rich and -neutral benzylic electrophiles have been developed, and the scope of the reaction has been explored with respect to both reaction partners. The high levels of asymmetric induction, as well as the reactivity pattern of the electrophiles, suggest an ?(3) -benzyl intermediate that arises through two distinct pathways. PMID:24115047

Trost, Barry M; Czabaniuk, Lara C

2013-09-25

140

Thermodynamic limitations on microbially catalyzed reaction rates  

NASA Astrophysics Data System (ADS)

Quantification of global biogeochemical cycles requires knowledge of the rates at which microorganisms catalyze chemical reactions. In order for models that describe these processes to capture global patterns of change, the underlying formulations in them must account for biogeochemical transformations over seasonal and millennial time scales in environments characterized by different energy levels. Building on existing models, a new thermodynamic limiting function is introduced. With only one adjustable parameter, this function that can be used to model microbial metabolism throughout the range of conditions in which organisms are known to be active. The formulation is based on a comparison of the amount of energy available from any redox reaction to the energy required to maintain a membrane potential, a proxy for the minimum amount of energy required by an active microorganism. This function does not require species- or metabolism-specific parameters, and can be used to model metabolisms that capture any amount of energy. The utility of this new thermodynamic rate limiting term is illustrated by applying it to three low-energy processes: fermentation, methanogenesis and sulfate reduction. The model predicts that the rate of fermentation will be reduced by half once the Gibbs energy of the catalyzed reaction reaches -12 kJ (mol e-)-1, and then slowing exponentially until the energy yield approaches zero. Similarly, the new model predicts that the low energy yield of methanogenesis, -4 to -0.5 kJ (mol e-)-1, for a partial pressure of H2 between 11 and 0.6 Pa decreases the reaction rate by 95-99%. Finally, the new function's utility is illustrated through its ability to accurately model sulfate concentration data in an anoxic marine sediment.

LaRowe, Douglas E.; Dale, Andrew W.; Amend, Jan P.; Van Cappellen, Philippe

2012-08-01

141

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

SciTech Connect

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.

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

2003-08-24

142

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

PubMed Central

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

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

2006-01-01

143

Nickel-Catalyzed Reductive Carboxylation of Styrenes Using CO2  

PubMed Central

A nickel catalyzed reductive carboxylation of styrenes using CO2 has been developed. The reaction proceeds under mild conditions using diethylzinc as the reductant. Preliminary data suggests the mechanism involves two discrete nickel-mediated catalytic cycles, the first involving a catalyzed hydrozincation of the alkene followed by a second, slower nickel-catalyzed carboxylation of the in situ formed organozinc reagent. Importantly, the catalyst system is very robust and will fixate CO2 in good yield even if exposed to only an equimolar amount introduced into the headspace above the reaction.

Williams, Catherine M.; Johnson, Jeffrey B.; Rovis, Tomislav

2010-01-01

144

Biotransformations catalyzed by the genus rhodococcus  

SciTech Connect

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

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

1994-01-01

145

Mechanisms of bacterially catalyzed reductive dehalogenation  

SciTech Connect

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.

Picardal, F.W.

1992-12-31

146

Iridium-Catalyzed Hydrogen Transfer Reactions  

NASA Astrophysics Data System (ADS)

This chapter describes the application of iridium complexes to catalytic hydrogen transfer reactions. Transfer hydrogenation reactions provide an alternative to direct hydrogenation for the reduction of a range of substrates. A hydrogen donor, typically an alcohol or formic acid, can be used as the source of hydrogen for the reduction of carbonyl compounds, imines, and alkenes. Heteroaromatic compounds and even carbon dioxide have also been reduced by transfer hydrogenation reactions. In the reverse process, the oxidation of alcohols to carbonyl compounds can be achieved by iridium-catalyzed hydrogen transfer reactions, where a ketone or alkene is used as a suitable hydrogen acceptor. The reversible nature of many hydrogen transfer processes has been exploited for the racemization of alcohols, where temporary removal of hydrogen generates an achiral ketone intermediate. In addition, there is a growing body of work where temporary removal of hydrogen provides an opportunity for using alcohols as alkylating agents. In this chemistry, an iridium catalyst "borrows" hydrogen from an alcohol to give an aldehyde or ketone intermediate, which can be transformed into either an imine or alkene under the reaction conditions. Return of the hydrogen from the catalyst provides methodology for the formation of amines or C-C bonds where the only by-product is typically water.

Saidi, Ourida; Williams, Jonathan M. J.

147

Titanium Catalyzed Perchlorate Reduction and Applications  

SciTech Connect

This work provides a proof-of-principle demonstration that Ti(III)-catalyzed electrochemical techniques could potentially be used for reduction of ClO{sub 4}{sup -} in small waste streams, such as the regeneration of selective anion-exchange resins that are loaded with ClO{sub 4}{sup -}. The technique may not be directly applied for the treatment of large volumes of ClO{sub 4}{sup -}-contaminated water at relatively low concentrations because of its slow reaction kinetics and the use of chemical reagents. Further studies are needed to optimize the reaction conditions in order to achieve a complete reduction of ClO{sub 4}{sup -} and the regeneration of spent resin beds. Alternative complexing and reducing agents may be used to enhance the reaction completeness of sorbed ClO{sub 4}{sup -} in the resin and to overcome potential clogging of micropores within the resin beads resulting from the precipitation of TiO{sub 2}.

Gu, Baohua [ORNL; Bonnesen, Peter V [ORNL; Sloop Jr, Frederick {Fred} V [ORNL; Brown, Gilbert M [ORNL

2006-01-01

148

Double parallel dynamic resolution through lipase-catalyzed asymmetric transformation.  

PubMed

Dynamic systems based on double parallel reactions have been generated and resolved in situ by secondary lipase-catalyzed asymmetric transformation, resulting in high chemo- and enantioselectivities. PMID:23348957

Zhang, Yan; Hu, Lei; Ramström, Olof

2013-01-25

149

Recent developments in gold-catalyzed cycloaddition reactions  

PubMed Central

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

2011-01-01

150

Flame Synthesis Used to Create Metal-Catalyzed Carbon Nanotubes.  

National Technical Information Service (NTIS)

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...

R. L. VanderWal

2001-01-01

151

Chemical Dehalogenation Treatment: Base-Catalyzed Decomposition Process (BCDP).  

National Technical Information Service (NTIS)

The Base-Catalyzed Decomposition Process (BCDP) is an efficient, relatively inexpensive treatment process for polychlorinated biphenyls (PCBs). It is also effective on other halogenated contaminants such as insecticides, herbicides, pentachlorophenol (PCP...

1992-01-01

152

Iron-catalyzed preparation of trifluoromethyl substituted vinyl- and alkynylcyclopropanes.  

PubMed

A convenient iron-catalyzed procedure to prepare trifluoromethylated vinyl- and alkynylcyclopropanes in a chemo- and diastereoselective manner is presented. The active diazo compound (trifluoromethyl diazomethane) is generated in situ and used in the concomitant cyclopropanation reaction. PMID:21591649

Morandi, Bill; Cheang, Jeremy; Carreira, Erick M

2011-05-17

153

Lysozyme Catalyzes the Formation of Antimicrobial Silver Nanoparticles (POSTPRINT).  

National Technical Information Service (NTIS)

Hen egg white lysozyme acted as the sole reducing agent and catalyzed the formation of silver nanoparticles in the presence of light. Stable silver colloids formed after mixing lysozyme and silver acetate in methanol and the resulting nanoparticles were c...

D. M. Eby G. R. Johnson K. E. Farrington N. M. Schaeublin S. M. Hussain

2009-01-01

154

Palladium-catalyzed carboxylative coupling of allylstannanes and allyl halides  

SciTech Connect

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

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

2000-04-17

155

Rhodium-Catalyzed Dehydrogenative Borylation of Cyclic Alkenes  

PubMed Central

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 cross-coupling applications are also presented.

Kondoh, Azusa; Jamison, Timothy F.

2010-01-01

156

Lanthanum Tricyanide-Catalyzed Acyl Silane-Ketone Benzoin Additions  

PubMed Central

Lanthanum tricyanide efficiently catalyzes a benzoin-type coupling between acyl silanes and ketones. Yields range from moderate to excellent over a broad substrate scope encompassing aryl, alkyl, electron-rich, and sterically hindered ketones.

Tarr, James C.; Johnson, Jeffrey S.

2009-01-01

157

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

National Technical Information Service (NTIS)

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

M. N. Rosenbluth S. Eliezer T. Tajima

1986-01-01

158

The Iron-Catalyzed Oxidation of Hydrazine by Nitric Acid  

SciTech Connect

To assess the importance of iron to hydrazine stability, the study of hydrazine oxidation by nitric acid has been extended to investigate the iron-catalyzed oxidation. This report describes those results.

Karraker, D.G.

2001-07-17

159

Hypervalent iodine-catalyzed oxylactonization of ketocarboxylic acids to ketolactones.  

PubMed

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

Uyanik, Muhammet; Yasui, Takeshi; Ishihara, Kazuaki

2009-04-05

160

Regioselective palladium-catalyzed intramolecular oxidative aminofluorination of unactivated alkenes.  

PubMed

A novel Pd-catalyzed regioselective intramolecular aminofluorination of unactivated alkenes has been developed, which is an efficient method for the synthesis of a variety of monofluoromethylated nitrogen-containing heterocycles. PMID:23955256

Wu, Tao; Cheng, Jiashun; Chen, Pinhong; Liu, Guosheng

2013-08-29

161

Enzyme-catalyzed regioselective transesterification of peracylated sophorolipids  

Microsoft Academic Search

Regioselective transesterifications and hydrolysis of peracylated sophorolipid (SL) derivatives catalyzed by lipases was investigated. This study is the first evaluation of the lipase-catalyzed reactions on the non-lactonic SL derivatives. Four lipases, namely from porcine pancreas (PPL, Type II), Candida rugosa (AYS, TypeVII), Pseudomonas cepacia (PS-30), and Candida antarctica (Novozym 435, carrier fixed lipase fraction B) were used in anhydrous THF

Jason A Carr; Kirpal S Bisht

2003-01-01

162

Lipolase catalyzed synthesis of benzyl esters of fatty acids  

Microsoft Academic Search

Lipolase 100 L, the lipase from the genetically engineered species of Aspergillus oryzae, has been used to catalyze esterification of lauric acid with aromatic alcohol—benzyl alcohol. A kinetic model for the lipase-catalyzed esterification in a biphasic organic–aqueous system has been proposed. Based on the interfacial substrate concentration, an analytical rate equation for initial rate of the reaction was derived and

M. S. Shintre; R. S. Ghadge; S. B. Sawant

2002-01-01

163

Mechanism of enzyme-catalyzed phospho group transfer  

SciTech Connect

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

Hansen, D.E.

1986-01-01

164

Sequential ruthenium-catalyzed hydroamination and rhenium-catalyzed C-H bond activation leading to indene derivatives.  

PubMed

[reaction: see text] Formal [3 + 2] annulation of arylacetylenes and alpha,beta-unsaturated carbonyl compounds is achieved in a one-pot reaction by successive treatment of the acetylenes with aniline and a catalytic amount of Ru(3)(CO)(12) and NH(4)PF(6) and C-H bond activation catalyzed by [ReBr(CO)(3)(thf)](2). The result suggests that the second rhenium-catalyzed indene formation is not disturbed by the first catalyst system. PMID:16774283

Kuninobu, Yoichiro; Nishina, Yuta; Takai, Kazuhiko

2006-06-22

165

Nitroreductase catalyzed biotransformation of CL-20.  

PubMed

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

Bhushan, Bharat; Halasz, Annamaria; Hawari, Jalal

2004-09-10

166

Highly efficient palladium-catalyzed hydrostannation of ethyl ethynyl ether  

PubMed Central

The palladium-catalyzed hydrostannation of acetylenes is widely exploited in organic synthesis as a means of forming vinyl stannanes for use in palladium-catalyzed cross-coupling reactions. Application of this methodology to ethyl ethynyl ether results in an enol ether that is challenging to isolate from the crude reaction mixture because of incompatibility with typical silica gel chromatography. Reported here is a highly efficient procedure for the palladium-catalyzed hydrostannation of ethyl ethynyl ether using 0.1% palladium(0) catalyst and 1.0 equiv of tributyltin hydride. The product obtained is a mixture of regioisomers that can be carried forward with exclusive reaction of the ?-isomer. This method is highly reproducible; relative to previously reported procedures, it is more economical and involves a more facile purification procedure.

Andrews, Ian P.; Kwon, Ohyun

2008-01-01

167

Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO  

SciTech Connect

Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, the author synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, they were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of the studies, he synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led them to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides. This report contains the Introduction; ``Chapter 6: Isomerization of Propargylic Alcohols to Enones and Enals Catalyzed by Methylrhenium Trioxide``; and Conclusions.

Jacob, J.

1999-05-10

168

Selective oxidation of Zn2+ -insulin catalyzed by Cu2+.  

PubMed

The purpose of this study is to quantitate the sensitivity of Zn2+ -insulin to oxidation catalyzed by various redox active transition metals, Cu2+, Fe2+, Mn2+, Ni2+, Co2+, Cr3+. Human recombinant insulin (INS) was subjected to oxidation under various conditions in the presence and absence of Zn2+ and ascorbate. The extent of oxidation was monitored by RP-HPLC. Only Cu2+, but none of the other metals or combination thereof, for example, Ni2+/Co2+, Co2+/Cr3+, and Ni2+/Cr3+, catalyzed INS oxidation, for example, to an extent of 45% when 20 microM INS/8.8 microM Zn2+ were exposed to 8 microM Cu2+ and 50 microM ascorbate for 90 min. The Cu2+ -catalyzed oxidation mainly targeted the B chain of INS, where the two histidine residues are located. PMID:17497728

Sadineni, Vikram; Schöneich, Christian

2007-07-01

169

Platinum-catalyzed C-h arylation of simple arenes.  

PubMed

This report describes the Na2PtCl4 catalyzed C-H arylation of arene substrates with diaryliodonium salts. The site selectivity of these reactions is predominantly controlled by steric factors. Remarkably, Na2PtCl4-catalyzed naphthalene arylation proceeds with opposite site selectivity compared to that obtained with Na2PdCl4 as the catalyst. Preliminary mechanistic studies provide evidence for a Pt(II)/Pt(IV) catalytic cycle involving rate-limiting C-C bond-forming reductive elimination. PMID:24125480

Wagner, Anna M; Hickman, Amanda J; Sanford, Melanie S

2013-10-15

170

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles  

SciTech Connect

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

Qinhua Huang

2004-12-19

171

Molecular Mechanism by which One Enzyme Catalyzes Two Reactions  

NASA Astrophysics Data System (ADS)

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.

Nishimasu, Hiroshi; Fushinobu, Shinya; Wakagi, Takayoshi

172

Gold-catalyzed highly enantioselective synthesis of axially chiral allenes.  

PubMed

Axially chiral allenes are synthesized from chiral propargylamines catalyzed by KAuCl4 in high yields (up to 93% yield) and excellent enantioselectivities (up to 97% ee) in CH3CN at 40 degrees C. The reaction has been applied to the synthesis of novel allene-modified artemisinin derivatives with the delicate endoperoxide moieties remaining intact. A tentative mechanism regarding gold(I)-catalyzed intramolecular hydride transfer was proposed on the basis of deuterium-labeling experiments and ESI-MS analysis of the reaction mixture. PMID:18181641

Lo, Vanessa Kar-Yan; Wong, Man-Kin; Che, Chi-Ming

2008-01-09

173

Esterification of phenolic acids catalyzed by lipases immobilized in organogels.  

PubMed

Lipases from Rhizomucor miehei and Candida antarctica B were immobilized in hydroxypropylmethyl cellulose organogels based on surfactant-free microemulsions consisting of n-hexane, 1-propanol and water. Both lipases kept their catalytic activity, catalyzing the esterification reactions of various phenolic acids including cinnamic acid derivatives. High reaction rates and yields (up to 94%) were obtained when lipase from C. antarctica was used. Kinetic studies have been performed and apparent kinetic constants were determined showing that ester synthesis catalyzed by immobilized lipases occurs via the Michaelis-Menten mechanism. PMID:20490615

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

2010-05-21

174

Radiation catalyzed conversion of tritium gas to tritiated water  

SciTech Connect

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

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

1983-01-01

175

N-Heterocyclic Carbene-Catalyzed Conjugate Additions of Alcohols  

PubMed Central

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

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

2010-01-01

176

Coalification by clay-catalyzed oligomerization of plant monomers  

SciTech Connect

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

Orchin, M.; Wilson, R.M.

1990-01-01

177

Peroxidase-Catalyzed Oxidation of 2,4,6Trichlorophenol  

Microsoft Academic Search

.   2,4,6-Trichlorophenol (TCP) is an environmental contaminant that is toxic, mutagenic, and carcinogenic. We have investigated\\u000a peroxidase-catalyzed oxidation of TCP as an alternative pathway of TCP bioactivation using horseradish peroxidase (HRP) as\\u000a a model peroxidase. TCP was shown to function as a reducing substarte for HRP as evidenced by TCP-dependent, HRP-catalyzed\\u000a reduction of 5-phenyl-4-penten-1-yl hydroperoxide (PPHP) to its corresponding alcohol.

F. W. Wiese; H. C. Chang; R. V. Lloyd; J. P. Freeman; V. M. Samokyszyn

1998-01-01

178

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

National Technical Information Service (NTIS)

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

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

1999-01-01

179

Engineering of Lipsa-Catalyzed Conversion in Organic Solvents Containing Ammonium Salts.  

National Technical Information Service (NTIS)

Contents: Introduction; Competitive lipase-catalyzed ester hydrolysis and ammoniolysis in organic solvents; equilibrium model of a solid-liquid-vapor system; Synthesis of primary amides by lipase-catalyzed amidation of carboxylic acids with ammonium salts...

M. J. J. Litjens

2000-01-01

180

Thermodynamic Property Values for Enzyme-catalyzed Reactions  

Microsoft Academic Search

This chapter deals with how one can obtain values of thermodynamic properties - specifically the apparent equilibrium constant K', the stan- dard molar transformed Gibbs energy change DrG', and the standard molar transformed enthalpy change DrH' for biochemical reactions - and, in particular, for enzyme-catalyzed reactions. In addition to direct measurement, these property values can be obtained in a variety

Robert N. Goldberg

2008-01-01

181

Pd-Catalyzed C-H Fluorination with Nucleophilic Fluoride  

PubMed Central

The palladium-catalyzed C–H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.

McMurtrey, Kate B.; Racowski, Joy M.; Sanford, Melanie S.

2012-01-01

182

Rhodium-catalyzed boron arylation of 1,2-azaborines.  

PubMed

A Sn-phony in B! BN isosteres of biphenyl compounds are prepared through Rh-catalyzed cross-coupling between 2-chloro-1,2-azaborines and arylstannanes. The synthetic method should enable investigations of structure-activity relationships (SARs) by expanding the chemical space of the pharmaceutically relevant biphenyl structure through BN/CC isosterism. PMID:23832871

Rudebusch, Gabriel E; Zakharov, Lev N; Liu, Shih-Yuan

2013-07-05

183

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

PubMed

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

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

2013-03-13

184

Oxidation reactions catalyzed by vanadium chloroperoxidase from Curvularia inaequalis  

Microsoft Academic Search

Vanadium haloperoxidases have been reported to mediate the oxidation of halides to hypohalous acid and the sulfoxidation of organic sulfides to the corresponding sulfoxides in the presence of hydrogen peroxide. However, traditional heme peroxidase substrates were reported not to be oxidized by vanadium haloperoxidases. Surprisingly, we have now found that the recombinant vanadium chloroperoxidase from the fungus Curvularia inaequalis catalyzes

Hilda B ten Brink; Henk L Dekker; Hans E Schoemaker; Ron Wever

2000-01-01

185

A Variation in Acid-Catalyzed Isomerization of Abietadienoic Acids  

Microsoft Academic Search

Heating the individual common abietadienoic acid methyl esters with p-toluene sulfonic acid in chloroform led to the formation of methyl abietadienoates other than the equilibrium mixture of methyl abietate, palustrate, and neoabietate that is usually formed by acid-catalyzed isomerization. Of these other methyl abietadienoates, the three principal constituents comprised 10%, 4% and 2% of the monomers; these compounds were isolated

Duane F. Zinkel

1991-01-01

186

Metal-catalyzed crystallization of amorphous carbon to graphene  

Microsoft Academic Search

Metal-catalyzed crystallization of amorphous carbon to graphene by thermal annealing is demonstrated. In this ``limited source'' process scheme, the thickness of the precipitated graphene is directly controlled by the thickness of the initial amorphous carbon layer. This is in contrast to chemical vapor deposition processes, where the carbon source is virtually unlimited and controlling the number of graphene layers depends

Maxwell Zheng; Kuniharu Takei; Benjamin Hsia; Hui Fang; Xiaobo Zhang; Nicola Ferralis; Hyunhyub Ko; Yu-Lun Chueh; Yuegang Zhang; Roya Maboudian; Ali Javey

2010-01-01

187

Acetylation of glycerol catalyzed by different solid acids  

Microsoft Academic Search

This work describes the acetylation of glycerol with acetic acid catalyzed by different solid acids. Reactions were carried out in batch mode under reflux. The kinetics of glycerol transformation and selectivity to the products, notably mono, di and triacetyl esters, were determined within 30min of reaction time to observe the primary products. The results showed that the acid exchange resin,

Valter L. C. Gonçalves; Bianca P. Pinto; João C. Silva; Claudio J. A. Mota

2008-01-01

188

Acid-catalyzed dehydrogenation of amine-boranes  

SciTech Connect

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

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

2010-01-12

189

Gold-catalyzed propargylic substitutions: Scope and synthetic developments  

PubMed Central

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

Debleds, Olivier; Gayon, Eric; Vrancken, Emmanuel

2011-01-01

190

Kinetic resolution of secondary alcohols catalyzed by chiral phosphoric acids.  

PubMed

Acid instead of base: Kinetic resolution of secondary alcohols is realized using chiral Brønsted acid catalyzed acylation instead of the conventional basic conditions. A broad range of functional groups are tolerated, such as aldehydes, carboxylic acids, and enoates. The selectivity factor (s) reaches up to 215 at ambient temperature. PMID:23940027

Harada, Shingo; Kuwano, Satoru; Yamaoka, Yousuke; Yamada, Ken-Ichi; Takasu, Kiyosei

2013-08-12

191

Nickel-catalyzed cycloaddition of anthranilic acid derivatives to alkynes.  

PubMed

A nickel-catalyzed cycloaddition has been developed where readily available anthranilic acid derivatives react with alkynes to afford substituted indoles. The reaction involves oxidative addition of Ni(0) to an ester moiety, which allows intermolecular addition to alkynes via decarbonylation and 1,3-acyl migration. PMID:21302974

Maizuru, Nobuyoshi; Inami, Tasuku; Kurahashi, Takuya; Matsubara, Seijiro

2011-02-04

192

Palladium-Catalyzed N-Arylation of 2-Aminothiazoles  

PubMed Central

A method for the Pd-catalyzed coupling of 2-aminothiazole derivatives with aryl bromides and triflates is described. Significantly, for this class of nucleophiles, the coupling exhibits a broad substrate scope and proceeds with a reasonable catalyst loading. Furthermore, an interesting effect of acetic acid as an additive is uncovered that facilitates catalyst activation.

McGowan, Meredeth A.; Henderson, Jaclyn L.

2012-01-01

193

Kinetics of acid-catalyzed cleavage of cumene hydroperoxide  

Microsoft Academic Search

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

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

2006-01-01

194

Gold(III)-catalyzed direct nucleophilic substitution of propargylic alcohols  

Microsoft Academic Search

Gold-catalyzed nucleophilic substitution of propargylic alcohols with various nucleophiles (allylsilane, electron-rich aromatics, alcohols, thiols, hydrides, 1,3-dicarbonyl derivatives, sulfonamides) is described under very mild conditions (room temperature in dichloromethane). Preliminary mechanistic investigations suggest a mechanism through a carbocation intermediate. Nucleophilic substitutions on allylic and benzylic alcohols are also described.

Marie Georgy; Valérie Boucard; Olivier Debleds; Christophe Dal Zotto; Jean-Marc Campagne

2009-01-01

195

Generalized rate equation for single-substrate enzyme catalyzed reactions  

Microsoft Academic Search

The most widely used rate expression for single-substrate enzyme catalyzed reactions, namely the Michaelis–Menten kinetics is based upon the assumption that enzyme concentration is in excess of the substrate in the medium and the rate is mainly limited by the substrate concentration according to saturation kinetics. However, this is only a special case and the actual rate expression varies depending

Fikret Kargi

2009-01-01

196

Iron-Catalyzed Heterocycle and Arene Deprotonative Alkylation  

PubMed Central

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

Tran, Ly Dieu; Daugulis, Olafs

2010-01-01

197

Stereoselective palladium-catalyzed allylic alkylations of peptide amide enolates.  

PubMed

Pd-catalyzed allylations are an excellent tool for stereoselective peptide modifications, being clearly superior to normal alkylations. The reactions proceed not only in high yield, but also high regio- and diastereoselectivities, and trans-products are formed exclusively. Therefore, this is a powerful synthetic tool for natural product and drug synthesis. PMID:21125093

Datta, Swarup; Kazmaier, Uli

2010-12-01

198

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles  

PubMed Central

Reaction of a monosubstituted, 1,3-disubstituted, or tetrasubstituted allene with various indoles catalyzed by a 1:1 mixture of a gold(I) N-heterocyclic carbene complex and AgOTf at room temperature leads to hydroarylation with formation of 3-allyl-indoles in modest to good yield.

Toups, Kristina L.; Liu, Gordon T.; Widenhoefer, Ross A.

2009-01-01

199

Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles  

PubMed Central

Reaction of a monosubstituted, 1,3-disubstituted, or tetrasubstituted allene with various indoles catalyzed by a 1:1 mixture of a gold(I) N-heterocyclic carbene complex and AgOTf at room temperature leads to hydroarylation with formation of 3-allyl-indoles in modest to good yield.

Toups, Kristina L.; Liu, Gordon T.; Widenhoefer, Ross A.

2010-01-01

200

Adventures in Gold-Catalyzed Cascade Reactions and Rearrangements  

Microsoft Academic Search

Gold-catalyzed organic transformations have been a hot topic of research in synthetic organic community over the last few years. Amazingly, most of the reactions can be performed under mild conditions using a catalytic amount of gold complexes. One of the widely reported reactions using gold catalysts is heterocyclization that involves an activation of a pi-system followed by a nucleophilic attack

Dinesh Vinod Vidhani

2010-01-01

201

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-?-lactams  

PubMed Central

Summary New gold-catalyzed methods using the ?-lactam scaffold have been recently developed for the synthesis of different sized heterocycles. This overview focuses on heterocyclization reactions of allenic and alkynic ?-lactams which rely on the activation of the allene and alkyne component. The mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed.

2011-01-01

202

Metal-Catalyzed Cleavage of tRNA[superscript Phe  

ERIC Educational Resources Information Center

|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]…

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

2008-01-01

203

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

National Technical Information Service (NTIS)

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

R. H. Hooverman

1979-01-01

204

Solvent-free lipase-catalyzed preparation of diacylglycerols.  

PubMed

Various methods have been applied for the enzymatic preparation of diacylglycerols that are used as dietary oils for weight reduction in obesity and related disorders. Interesterification of rapeseed oil triacylglycerols with commercial preparations of monoacylglycerols, such as Monomuls 90-O18, Mulgaprime 90, and Nutrisoft 55, catalyzed by immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) in vacuo at 60 degrees C led to extensive (from 60 to 75%) formation of diacylglycerols. Esterification of rapeseed oil fatty acids with Nutrisoft, catalyzed by Lipozyme RM in vacuo at 60 degrees C, also led to extensive (from 60 to 70%) formation of diacylglycerols. Esterification of rapeseed oil fatty acids with glycerol in vacuo at 60 degrees C, catalyzed by Lipozyme RM and lipases from Thermomyces lanuginosus (Lipozyme TL IM) and Candida antarctica (lipase B, Novozym 435), also provided diacylglycerols, however, to a lower extent (40-45%). Glycerolysis of rapeseed oil triacylglycerols with glycerol in vacuo at 60 degrees C, catalyzed by Lipozyme TL and Novozym 435, led to diacylglycerols to the extent of

Weber, Nikolaus; Mukherjee, Kumar D

2004-08-25

205

Oxygen Transfer to Ethylene Catalyzed by the Ag(110) Surface.  

National Technical Information Service (NTIS)

The silver surface catalyzed epoxidation of ethylene using molecular oxygen as an oxygen donor been studied using extended Huckel calculations. Five types of absorbed molecular oxygen on an Ag(110) surface have been considered, an end-on adsorption on top...

K. A. Jorgensen R. Hoffmann

1989-01-01

206

Triptycenediols by rhodium-catalyzed [2+2+2] cycloaddition.  

PubMed

An efficient, modular synthesis of triptycene derivatives is presented, in which the triptycene ring system is constructed from readily available anthraquinone and alkyne starting materials. A rhodium-catalyzed alkyne cyclotrimerization reaction serves as the key step in this new method for the preparation of these useful unnatural products. PMID:17685536

Taylor, Mark S; Swager, Timothy M

2007-08-08

207

CU(II): catalyzed hydrazine reduction of ferric nitrate  

SciTech Connect

A method is described for producing ferrous nitrate solutions by the cupric ion-catalyzed reduction of ferric nitrate with hydrazine. The reaction is complete in about 1.5 hours at 40/sup 0/C. Hydrazoic acid is also produced in substantial quantities as a reaction byproduct.

Karraker, D.G.

1981-11-01

208

Cu(II) - Catalyzed Hydrazine Reduction of Ferrous Nitrate  

SciTech Connect

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

Karraker, D.G.

2001-10-15

209

Photoresist Removal using Atomic Hydrogen Generated by Heated Catalyzer  

Microsoft Academic Search

In this paper, a novel method for high-dose ion-implanted photoresist removal using atomic hydrogen generated by a heated tungsten catalyzer is proposed. It is found that photoresist doped as high as 1× 1015 cm-2 can be removed completely. Quadruple mass spectroscopy detected hydrocarbon fragments during the atomic hydrogen treatment.

Akira Izumi; Hideki Matsumura

2002-01-01

210

Platinum-catalyzed oxoarylations of ynamides with nitrones.  

PubMed

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

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

2012-10-22

211

Novobiocin and Coumermycin Inhibit DNA Supercoiling Catalyzed by DNA Gyrase  

Microsoft Academic Search

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

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

1976-01-01

212

Palladium-Catalyzed Asymmetric Hydrogenation of ?-Acyloxy-1-arylethanones.  

PubMed

First hand: The first example of a palladium-catalyzed asymmetric hydrogenation of ?-acyloxy ketones (1) was accomplished to give the hydrogenated products 2 with by far the highest catalytic efficiency in up to quantitative conversions and excellent enantioselectivities. The hydrogenated products could serve as important intermediates for the preparation of many drug candidates. TFE=2,2,2-trifluoroethanol. PMID:24038964

Chen, Jianzhong; Liu, Delong; Butt, Nicholas; Li, Chao; Fan, Dongyang; Liu, Yangang; Zhang, Wanbin

2013-09-13

213

Palladium-Catalyzed Coupling Reactions of Aryl Chlorides  

Microsoft Academic Search

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

Adam F. Littke; Gregory C. Fu

2002-01-01

214

Transition-Metal-Catalyzed Carbonylation of Methyl Acetate.  

ERIC Educational Resources Information Center

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

Polichnowski, S. W.

1986-01-01

215

Enhancement of photosensitivity in the alcohol-added ferroin-catalyzed Belousov-Zhabotinsky reaction system  

Microsoft Academic Search

The observation of photoinduced image formation in the alcohol-added ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction is reported. It is found that alcohol acts as a reagent that reduces the activation energy both of the ferroin-catalyzed and the Ce-catalyzed BZ reaction system and enhances the photosensitivity. By comparing the photosensitivity and photoinduced image formation for the ferroin-catalyzed BZ system with and without alcohol,

Jiro Abe; Kazuhisa Matsuda; Masakazu Taka; Yasuo Shirai

1995-01-01

216

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

ERIC Educational Resources Information Center

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

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

2006-01-01

217

Structural basis for Diels-Alder ribozyme-catalyzed carbon-carbon bond formation  

Microsoft Academic Search

The majority of structural efforts addressing RNA's catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with

Alexander Serganov; Sonja Keiper; Lucy Malinina; Valentina Tereshko; Eugene Skripkin; Claudia Höbartner; Anna Polonskaia; Anh Tuân Phan; Richard Wombacher; Ronald Micura; Zbigniew Dauter; Andres Jäschke; Dinshaw J Patel

2005-01-01

218

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

ERIC Educational Resources Information Center

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

Lombardo, Anthony

1982-01-01

219

Role of Homoserine Transacetylase as a New Target for Antifungal Agents  

Microsoft Academic Search

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

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

2007-01-01

220

Asymmetric oxidoreductions catalyzed by alcohol dehydrogenase in organic solvents  

SciTech Connect

A methodology is developed for the use of alcohol dehydrogenase (and other NAD/sup +//NADH-dependent enzymes) as catalysts in organic solvents. The enzyme and the cofactor are deposited onto the surface of glass beads which are then suspended in a water-immiscible organic solvent containing the substrate. Both NADH and NAD/sup +/ are efficiently regenerated in such a system with alcohol dehydrogenase-catalyzed oxidation of ethanol and reduction of isobutyraldehyde, respectively; cofactor turnover numbers of 10/sup 5/ to greater than 10/sup 6/ have been obtained. With use of asymmetric oxidoreductions catalyzed by horse liver alcohol dehydrogenase in isopropyl ether, optically active (ee of 95 to 100%) alcohols and ketones have been prepared on a 1 to 10 mmol scale.

Grunwald, J.; Wirz, B.; Scollar, M.P.; Klibanov, A.M.

1986-10-15

221

Cholera toxin can catalyze ADP-ribosylation of cytoskeletal proteins  

SciTech Connect

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

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

1981-11-01

222

Rearrangement Reactions Catalyzed by Cytochrome P450s  

PubMed Central

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

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

2010-01-01

223

Ligand development in the Ni-catalyzed hydrocyanation of alkenes.  

PubMed

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

Bini, Laura; Müller, Christian; Vogt, Dieter

2010-10-25

224

Mechanism of combustion of catalyzed double base propellants  

SciTech Connect

Existing combustion models, namely, photo chemical theory, chelate and ..pi..-complex theory, and free radical mechanism and carbon/carbonaceous matter formation theory, for catalyzed double base propellants have been evaluated in the light of the experimental findings of the present study. Results obtained suggest that carbon formation and its availability to catalyze the reactions in foam and fizz zones are the probable cause of catalysis and platonization. It seems that both these phenomena (catalysis/platonization) are dependent on the C/NO ratio. So long as this ratio is above unity, the catalytic effect is observed, followed by the plateau effect, where this ratio is changed to unity. Ultimately, when the C/NO ratio is reduced to less than one, the burning rate falls and the postplateau effect is obtained.

Singh, H.; Rao, K.R.K.

1988-02-01

225

Mild and efficient cyanuric chloride catalyzed Pictet-Spengler reaction  

PubMed Central

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

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

2013-01-01

226

Generalized rate equation for single-substrate enzyme catalyzed reactions.  

PubMed

The most widely used rate expression for single-substrate enzyme catalyzed reactions, namely the Michaelis-Menten kinetics is based upon the assumption that enzyme concentration is in excess of the substrate in the medium and the rate is mainly limited by the substrate concentration according to saturation kinetics. However, this is only a special case and the actual rate expression varies depending on the initial enzyme/substrate ratio (E(0)/S(0)). When the substrate concentration exceeds the enzyme concentration the limitation is due to low enzyme concentration and the rate increases with the enzyme concentration according to saturation kinetics. The maximum rate is obtained when the initial concentrations of the enzyme and the substrate are equal. A generalized rate equation was developed in this study and special cases were discussed for enzyme catalyzed reactions. PMID:19265680

Kargi, Fikret

2009-03-03

227

Muonic three-body problem and muon- catalyzed fusion  

NASA Astrophysics Data System (ADS)

Recently, the muonic three-body system dt?, has aroused considerable attention in relation to the realization of a useful muon-catalyzed fusion [1, 2]. This bound system must be solved up to 6 digits in energy to establish the muon catalyzed fusion process. We applied the ATMS method [3] and the coupled-channel method [4] to the Coulomb three-body system and obtained the detailed information on the energy levels and the wave functions of the bound states. Further we investigated the effect of the nuclear interaction on the fusion rate in the bound states [5] and developed a formalism to calculate the muon sticking to4He [6]. In this paper we report the results obtained in our collaborations: Figure 2 shows up our main results.

Akaishi, Y.; Kamimura, M.; Narumi, H.

1987-03-01

228

Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.  

PubMed Central

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

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

1993-01-01

229

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides  

PubMed Central

Summary Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)]2 as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon–halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75–94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst.

Tigchelaar, Andrew

2012-01-01

230

Mechanism of rhodium-catalyzed carbene formation from diazo compounds.  

PubMed

[reaction: see text] A large and normal nitrogen-15 kinetic isotope effect of 1.035 +/- 0.003 provides direct support for the proposed mechanism for the rhodium-catalyzed carbene formation from diazo compounds, which involves the fast formation of a metal-diazo complex followed by rate-limiting extrusion of N2. The large magnitude of the KIE indicates extensive C-N bond fission in the transition state. PMID:17408276

Wong, Freeman M; Wang, Jianbo; Hengge, Alvan C; Wu, Weiming

2007-04-05

231

[Synthesis of carbohydrate related compounds by using aldolase catalyzed reaction].  

PubMed

Enzymes proceed the reaction with high regio- and stereoselectivity under mild conditions, i.e. in an aqueous medium at room temperature. However, enzymatic reactions that catalyze carbon-carbon bond formation have not been utilized in organic synthesis until recently. We had an interest in an aldolase-catalyzed reaction which proceed carbon-carbon bond formation referred to aldol condensation, by which many bioactive compounds have been rationally synthesized. On the other hand, recent biological studies on cell recognition (cell adhesion) have disclosed the important roles of oligosaccharides on cell surfaces, especially which include glucuronic acid, 3-deoxy-D-manno-oct-2-ulosonic acid (KDO), and sialic acid in the structures e.g., sialyl Lewis X and endotoxins, in differentiation, induction, viral and bacterial infections, and immune response. As well as acidic oligosaccharides, basic ones have been utilized as practical medicines in the clinical level, like acarbose that acts as an amylase inhibitor. Based on these background, we embarked the synthesis of carbohydrate related compounds which can control the interaction between carbohydrates and carbohydrate recognition protein by the use of several aldolases. Azasugars, potent inhibitors toward glycosidases, were synthesized using fructose-1,6-diphosphate (FDP)-aldolase and other dihdroxyacetonephosphate (DHAP)-dependent aldolases in the key step. Sialyl Lewis X mimetic, peptidic mimetic of RNA having anti-Vero toxin activity, mycestericin D, and aza-idulonic acid were prepared by taking advantage of L-threonine aldolase catalyzed reaction, which afford beta-hydroxy-alpha-L-amino acids. A precursor of KDO, featured acidic sugar of endotoxins was provided by the reaction catalyzed with kynureninase, which generates beta-anion of L-alanine in its active site during the metabolic reaction from kynurenine to anthranilic acid. PMID:10655781

Kajimoto, T

2000-01-01

232

Gold-catalyzed cyclization of allenyl acetal derivatives.  

PubMed

The gold-catalyzed transformation of allenyl acetals into 5-alkylidenecyclopent-2-en-1-ones is described. The outcome of our deuterium labeling experiments supports a 1,4-hydride shift of the resulting allyl cationic intermediates because a complete deuterium transfer is observed. We tested the reaction on various acetal substrates bearing a propargyl acetate, giving 4-methoxy-5-alkylidenecyclopent-2-en-1-ones 4 via a degradation of the acetate group at the allyl cation intermediate. PMID:24062838

Vasu, Dhananjayan; Pawar, Samir Kundlik; Liu, Rai-Shung

2013-08-27

233

Pd-Catalyzed Enantioselective Allyl-Allyl Cross Coupling  

PubMed Central

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

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

2010-01-01

234

Transition metal-catalyzed oxidations of bishomoallylic alcohols  

Microsoft Academic Search

In recent years, new transition metal-catalyzed reactions for chemo- and stereoselective oxidations of bishomoallylic alcohols have been developed. The role of transition metals in this catalysis is connected with (i) activation of a primary oxidant (e.g. molecular oxygen, hydrogen peroxide, or tert-butyl hydroperoxide—reactivity), (ii) direction of the alkenol oxidation into a specific reaction channel (chemoselectivity), and (iii) control of the

Jens Hartung; Marco Greb

2002-01-01

235

Nickel-Catalyzed Allylic Substitution of Simple Alkenes  

PubMed Central

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

Matsubara, Ryosuke; Jamison, Timothy F.

2011-01-01

236

Electrostatic effects on the rates of DNA-catalyzed reactions  

Microsoft Academic Search

Diol-epoxide metabolites of many genotoxic polycyclic aromatic hydrocarbons are hydrolyzed to tetraols in a detoxification reaction. The hydrolysis reaction has both spontaneous and acid-catalyzed components; moreover, the reaction rate increases in the presence of DNA. The best studied of these diol epoxide metabolites are the trans 7,8 diol-9,10 epoxides of benzo[a]pyrene: anti-BPDE, the proximate carcinogen, in which the oxirane ring

George R. Pack; Linda Wong

1996-01-01

237

Myoglobin-Catalyzed Tyrosine Nitration: No Need for Peroxynitrite  

Microsoft Academic Search

The nitration of tyrosine residues in protein to yield 3-nitrotyrosine derivatives has been suggested to represent a specific footprint for peroxynitrite formation in vivo. However, recent studies suggest that certain hemoproteins such as peroxidases catalyze the H2O2-dependent nitration of tyrosine to yield 3-nitrotyrosine in a peroxynitrite-independent reaction. Because 3-nitrotyrosine has been shown to be present in the postischemic myocardium, we

Kamer Kilinc; Asuman Kilinc; Robert E. Wolf; Matthew B. Grisham

2001-01-01

238

Gold(I)-Catalyzed Stereoconvergent, Intermolecular Enantioselective Hydroamination of Allenes  

PubMed Central

A 1:2 mixture of [(S)-2](AuCl)2 [(S)-2 = (S)-3,5-t-Bu-4-MeO-MeOBIPHEP] and AgBF4 catalyzes the stereoconvergent, intermolecular enantioselective hydroamination of chiral, racemic 1,3-disubstituted allenes with N-unsubstituted carbamates to form N-allylic carbamates in good yield, with high regio- and diastereoselectivity, and up to 92% ee.

Butler, Kristina L.; Tragni, Michele; Widenhoefer, Ross A.

2012-01-01

239

Aerobic oxychlorination of phenols catalyzed by copper(II) chloride  

Microsoft Academic Search

Oxychlorination of phenol and electron-rich phenolic compounds catalyzed by CuCl2 under mild conditions has been developed. Chloride ions are used as halogenating agents and dioxygen as a final oxidant. The catalyst shows not only high regioselectivity for para- or ortho isomers but also a remarkable chemoselectivity for monochlorination, with no products of the oxidation of phenols being formed in detectable

Luciano Menini; Elena V. Gusevskaya

2006-01-01

240

Gold-catalyzed cyclization of allenyl acetal derivatives  

PubMed Central

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

Vasu, Dhananjayan; Pawar, Samir Kundlik

2013-01-01

241

Base-Catalyzed Depolymerization of Lignin: Separation of Monomers  

Microsoft Academic Search

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

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

2007-01-01

242

Regiospecific oxidoreductions catalyzed by a new Pseudomonas paucimobilis hydroxysteroid dehydrogenase  

Microsoft Academic Search

The preparative-scale regio- and stereo-specific oxidation of hydroxy groups and reduction of keto functions at C(3) of several C21 bile acids, catalyzed by a new 3?-hydroxysteroid dehydrogenase (3?-HSDH), is reported. The crude enzyme, isolated from the cells of Pseudomonas paucimobilis, revealed the presence of a further enzymatic fraction containing a secondary alcohol dehydrogenase (SADH), that has been used to recycle

Ercolina Bianchini; Nicola Chinaglia; Mariangela Dean; Pier Paolo Giovannini; Alessandro Medici; Paola Pedrini; Silvia Poli

1999-01-01

243

Asymmetric oxidoreductions catalyzed by alcohol dehydrogenase in organic solvents  

Microsoft Academic Search

A methodology is developed for the use of alcohol dehydrogenase (and other NAD\\/sup +\\/\\/NADH-dependent enzymes) as catalysts in organic solvents. The enzyme and the cofactor are deposited onto the surface of glass beads which are then suspended in a water-immiscible organic solvent containing the substrate. Both NADH and NAD\\/sup +\\/ are efficiently regenerated in such a system with alcohol dehydrogenase-catalyzed

Jacob. Grunwald; Beat. Wirz; Mark P. Scollar; Alexander M. Klibanov

1986-01-01

244

Synthesis of substituted oxindoles by chloroperoxidase catalyzed oxidation of indoles  

Microsoft Academic Search

Chloroperoxidase catalyzed oxidation of substituted indoles yields the corresponding oxindoles in virtually quantitative yield. These include 5-chloro-oxindole, a precursor for the anti-inflammatory agent Tenidap, which was obtained in 95% yield. The reactivity of the substituted indoles depends on the nature and the position of the substituent. Both electronic and steric effects of substituents appear to be important. All of the

M. P. J van Deurzen; F van Rantwijk; R. A Sheldon

1996-01-01

245

Allylic oxidation of cyclohexene catalyzed by manganese porphyrins: DFT studies  

Microsoft Academic Search

The present paper summarizes density functional theory studies on hydroxylation of cyclohexene catalyzed by manganese oxo porphyrin. The reaction is preceded by the physisorption of the substrate over the catalyst molecule at the distance of 2.18Å. Next, a hydrogen atom form the C–H bond is abstracted by the catalyst oxo group and the cyclohexene radical is readily bound to the

D. Rutkowska-Zbik; M. Witko; E. M. Serwicka

2011-01-01

246

Asymmetric Ni-Catalyzed Conjugate Allylation of Activated Enones  

PubMed Central

The nickel-catalyzed enantioselective addition of allylboronic acid pinacol ester - allylB(pin) – is described. This reaction is highly effective with dialkylidene ketones and favors the allylation of the benzylidene site in non-symmetric substrates. The reaction appears to proceed by conversion of the dialkylidene ketone substrate to an unsaturated ?-allyl complex (I), followed by reductive elimination. Enantioselectivities range from 91–94% ee for a range of substrates when chiral ligand 14 is employed.

Sieber, Joshua D.; Morken, James P.

2011-01-01

247

Iridium-catalyzed alkylation of methylquinolines with alcohols.  

PubMed

Iridium-catalyzed alkylation of methylquinolines at the methyl substituent was achieved using alcohols as alkylating agents. The reaction proceeded through a transfer hydrogenation pathway from the alcohol to the Ir complex, affording an aldehyde and Ir-H species, followed by base-assisted aldol condensation and hydrogenation. This method provides an atom-economical and convenient route to alkylquinolines from easily accessible methylquinolines. PMID:23013149

Obora, Yasushi; Ogawa, Shinji; Yamamoto, Nobuyuki

2012-10-03

248

Gold-catalyzed oxidative cycloadditions to activate a quinoline framework.  

PubMed

Going for gold! Gold-catalyzed reactions of 3,5- and 3,6-dienynes with 8-alkylquinoline oxides results in an oxidative cycloaddition with high stereospecificity (see scheme; EWG = electron-withdrawing group); this process involves a catalytic activation of a quinoline framework. The reaction mechanism involves the intermediacy of ?-carbonyl pyridinium ylides (I) in a concerted [3+2]-cycloaddition with a tethered alkene. PMID:24038347

Huple, Deepak B; Ghorpade, Satish; Liu, Rai-Shung

2013-09-05

249

Oxidative bromination of aromatic compounds catalyzed by heteropoly acids  

SciTech Connect

Heteropoly acids with the composition H/sub 3+n/PMo/sub 12-n/V/sub n/O/sub 40/ catalyze the bromination of arenes in the ring in HOAc-H/sub 2/O solution when HBr and O/sub 2/ are used as the brominating agent. The reaction proceeds through the oxidation of Br/sup -/ to Br/sub 2/ by means of oxygen with p-HPA (p-heteropoly acids) as the catalysts.

Gorodetskays, T.A.; Kozhevnikov, I.V.; Matveev, K.I.

1983-02-01

250

Biaryl Phosphine Ligands in Palladium-Catalyzed Amination  

PubMed Central

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

Surry, David S.

2012-01-01

251

Superacidic FSO 3 H\\/HF catalyzed butane isomerization [1  

Microsoft Academic Search

Superacid catalyzed isomerization of butane was studied. Highly efficient isomerization of butane to 2-methylpropane (isobutane) was achieved using fluorosulfuric acid containing up to 5% of hydrogen fluoride acting as a protic co-acid. The isomerization when carried out in excess FSO3H at 21 ° C in a flow system gave ~70% conversion to 2-methylpropane with generally less than 3% cracking. When

George A. Olah; Omar Farooq; Altaf Husain; Ni Ding; Nirupam J. Trivedi; Judith A. Olah

1991-01-01

252

The gravitino-stau scenario after catalyzed big bang nucleosynthesis  

SciTech Connect

We consider the impact of catalyzed big bang nucleosynthesis on theories with a gravitino lightest superparticle and a charged slepton next-to-lightest superparticle. In models where the gravitino to gaugino mass ratio is bounded from below, such as gaugino-mediated supersymmetry breaking, we derive a lower bound on the gaugino mass parameter m{sub 1/2}. As a concrete example, we determine the parameter space of gaugino mediation that is compatible with all cosmological constraints.

Kersten, Joern [The Abdus Salam ICTP, Strada Costiera 11, 34014 Trieste (Italy); Schmidt-Hoberg, Kai, E-mail: jkersten@ictp.it, E-mail: kai.schmidt-hoberg@ph.tum.de, E-mail: kai.schmidt.hoberg@desy.de [Physik-Department T30, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching (Germany)

2008-01-15

253

Formation of aromatic chlorinated compounds catalyzed by copper and iron  

Microsoft Academic Search

This study shows the catalyzing effects of iron and copper on the formation of chlorinated compounds such as chlorobenzenes (ClBzs), chlorophenols (CIPhs), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). Both total concentrations and congener distributions have been studied. The parameters and conditions varied during the combustion tests were the complete and incomplete combustion and the metal and chlorine addition. The incomplete

Halonen Ismo; Tuppurainen Kari; Ruuskanen Juhani

1997-01-01

254

CeO 2 -catalyzed ozonation of phenol  

Microsoft Academic Search

Three different cerium citrate-based precursors were used for synthesizing CeO2 through thermal treatment. Three morphological types of CeO2 were obtained. Characterization of these oxides was carried out by XRD patterns, SEM microscopy, N2 adsorption isotherms, Raman spectroscopy, zeta potential, and UV\\/Vis luminescence. Ozonation of phenol catalyzed by CeO2 was studied as a representative reaction of environmental interest. The differences on

M. F. Pinheiro da Silva; L. S. Soeira; K. R. P. Daghastanli; T. S. Martins; I. M. Cuccovia; R. S. Freire; P. C. Isolani

2010-01-01

255

Sugar fatty acid ester surfactants: Base-catalyzed hydrolysis  

Microsoft Academic Search

Rate constants for the base-catalyzed hydrolysis of sucrose laurate, sucrose ?-sulfonyl laurate, and sucrose ?-ethyl laurate\\u000a were measured at several temperatures in pH 11 buffer. Activation energies and Arrhenius factors for the hydrolysis reactions\\u000a were determined. At 27C, sucrose laurate hydrolyzed fastest and sucrose ?-ethyl laurate slowest. Activation energies and\\u000a Arrhenius factors showed that both steric and electronic factors affect

Irene J. A. Baker; D. Neil Furlong; Franz Grieser; Calum J. Drummond

2000-01-01

256

Enzyme Catalyzed Regioselective Synthesis of Sucrose Fatty Acid Ester Surfactants  

Microsoft Academic Search

A commercial subtilisin preparation was used in pyridine to catalyze the regioselective conversion of sucrose and fatty acid vinyl esters into the 1?-O-acyl sucrose derivatives. The 1?-O-laury sucrose, 1?-O-myristyl sucrose and 1?-O-stearyl sucrose were obtained as the major products of these reactions. The 1?,6-di-O-acyl sucrose derivatives were also obtained as minor products. The critical micellar concentration (CMC) of each of

Tulay Polat; Hélène G. Bazin; Robert J. Linhardt

1997-01-01

257

Reductive dechlorination catalyzed by bacterial transition-metal coenzymes  

Microsoft Academic Search

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.

Charles J. Gantzer; Lawrence P. Wackett

1991-01-01

258

Hydroxynitrile Lyase-Catalyzed Enantioselective Conversion of Ketones into Cyanohydrins  

Microsoft Academic Search

In this thesis I have addressed several issues related to the HNL-catalyzed preparation of cyanohydrins. I first demonstrated in Chapter 2 that immobilized HNL as sol-gels and as commercially available Cross Linked Enzyme Aggregates (CLEA®) improved several features of the biocatalyst such as solvent stability, and substrate or product inhibition\\/deactivation. In particular, MeCLEA was remarkably stable towards the deleterious effect

F. L. Cabirol

2010-01-01

259

Silver-catalyzed radical phosphonofluorination of unactivated alkenes.  

PubMed

We report herein a mild and catalytic phosphonofluorination of unactivated alkenes. With catalysis by AgNO3, the condensation of various unactivated alkenes with diethyl phosphite and Selectfluor reagent in CH2Cl2/H2O/HOAc at 40 °C led to the efficient synthesis of ?-fluorinated alkylphosphonates with good stereoselectivity and wide functional group compatibility. A mechanism involving silver-catalyzed oxidative generation of phosphonyl radicals and silver-assisted fluorine atom transfer is proposed. PMID:24025164

Zhang, Chengwei; Li, Zhaodong; Zhu, Lin; Yu, Limei; Wang, Zhentao; Li, Chaozhong

2013-09-13

260

?-Amination of aldehydes catalyzed by in situ generated hypoiodite.  

PubMed

The metal-free amination of different aldehydes is catalyzed by hypoiodite, which is generated by employing commercially available sodium percarbonate as the co-oxidant. This approach has several advantages: it is a metal-free oxidation that works under mild reaction conditions; furthermore, it has a wide substrate scope and does not give toxic by-products from the co-oxidant that is used. PMID:22855029

Tian, Jie-Sheng; Ng, Kang Wai Jeffrey; Wong, Jiun-Ru; Loh, Teck-Peng

2012-07-31

261

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

PubMed Central

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

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

2009-01-01

262

Acetalization of Carbonyl Compounds Catalyzed by I2-Doped Polyaniline  

Microsoft Academic Search

Polyaniline-I2 is prepared by doping of polyaniline base with iodine. Polyaniline base and polyaniline-I2 are characterized by infrared spectra, X-ray diffraction spectra, and thermogravimetric analysis. Polyaniline-I2 is used as a catalyst for the first time in acetalization of carbonyl compounds. The catalyzing acetalization of cyclohexanone and propane-1,2-diol is conducted in excellent yields with simple and more environmental benign procedure. This

Genxiang Luo; Miao He; Zhaojin Zhong

2008-01-01

263

Aminoacyl-RNA Synthesis Catalyzed by an RNA  

NASA Astrophysics Data System (ADS)

An RNA has been selected that rapidly aminoacylates its 2'(3' terminus when provided with phenylalanyl-adenosine monophosphate. That is, the RNA accelerates the same aminoacyl group transfer catalyzed by protein aminoacyl-transfer RNA synthetases. The best characterized RNA reaction requires both Mg2+ and Ca2+. These results confirm a necessary prediction of the RNA world hypothesis and represent efficient RNA reaction (>=10^5 times accelerated) at a carbonyl carbon, exemplifying a little explored type of RNA catalysis.

Illangasekare, Mali; Sanchez, Giselle; Nickles, Tim; Yarus, Michael

1995-02-01

264

N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones†  

PubMed Central

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.

Atienza, Roxanne L.; Roth, Howard S.

2012-01-01

265

?-Type Glycosidic Bond Formation by Palladium-Catalyzed Decarboxylative Allylation.  

PubMed

Decarboxylative allylation of glycals: A ?-type glycosidic bond has been constructed in high regio- and stereoselectivity by means of a palladium-catalyzed decarboxylative O-glycosylation. Various kinds of glycals with different protecting groups have been examined for this reaction to afford a diverse set of glycosylated products, including phenolic O-glycosides, thiophenolic S-glycoside, aliphatic O-glycosides, and disaccharides with excellent ?-selectivity and reasonable to excellent yields. PMID:24108596

Xiang, Shaohua; Lu, Zhiqiang; He, Jingxi; Le Maihoang, Kim; Zeng, Jing; Liu, Xue-Wei

2013-09-17

266

Asymmetric Additions to Dienes Catalyzed by a Dithiophosphoric Acid  

PubMed Central

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

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

2011-01-01

267

Schistosoma mansoni: glutathione S-transferase-catalyzed detoxication of dichlorvos.  

PubMed

Dialyzed cytosol of adult Schistosoma mansoni worm pairs catalyzed the glutathione-dependent O-demethylation of dichlorvos (2,2-dichlorovinyl dimethylphosphate), the active form of the antischistosomal drug metrifonate, to form a thioether conjugate, S-methylglutathione, and desmethyl dichlorvos. The reaction rate was dependent on both time and protein concentration, and no product was formed when either dichlorvos or glutathione was omitted from the reaction mixture. Female worm cytosols were about 2.5-fold more active per milligram of protein that those of males. Partial purification of glutathione S-transferases from male worms by affinity chromatography on glutathione-agarose showed that the reaction could be catalyzed by a preparation containing the three major isoenzymes, but that the unbound fraction, which contains at least one additional form of the enzyme that is particularly active with epoxide substrates, was 16-fold more active toward dichlorvos than the bound fraction. S-Methylglutathione also was formed by S. mansoni worm pairs incubated in the presence but not in the absence of dichlorvos. Because GSH S-transferase-catalyzed metabolism of dichlorvos results in the formation of desmethyldichlorvos, which unlike the parent compound is not an effective acetylcholinesterase inhibitor, the reaction represents a pathway of detoxication in schistosomes. It is the first example of a clinically used schistosomicide shown to be detoxicated by a conjugation pathway. These results raise the possibility that dichlorvos detoxication by S. mansoni may help explain why this species is normally refractory to metrifonate. PMID:2026213

O'Leary, K A; Tracy, J W

1991-05-01

268

Protection of Wood from Microorganisms by Laccase-Catalyzed Iodination  

PubMed Central

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.

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

2012-01-01

269

Stau-catalyzed big-bang nucleosynthesis reactions  

SciTech Connect

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.

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

270

Reduction of nitrobenzene by the catalyzed Fe/Cu process.  

PubMed

The polarization behavior of the couple Fe/Cu in 100 mg/L nitrobenzene aqueous solution was studied using Evans coupling diagrams. The results indicated that the iron corrosion was limited by both anodic and cathodic half-cell reactions under the neutral conditions, and cathodically controlled under the alkaline conditions. Batch experiments were performed to study the effect of solution pH, reaction duration, concentration, type of electrolyte, and dissolved oxygen (DO) on the reduction of nitrobenzene by the catalyzed Fe/Cu process. This process proved effective in the pH range of 3 to 11. The conversion efficiency of nitrobenzene at pH around 10.1 was almost the same as that under highly acid conditions (pH around 3). The degradation of nitrobenzene fell into two phases: adsorption and surface reduction, and the influence of adsorption and mass transfer became more extensive with solution concentration. The reduction rate decreased in the presence of DO in the solution, indicating that a need for aeration was eliminated in the catalyzed Fe/Cu process. Accordingly, spending on energy consumption would be reduced. Economic analysis indicated that merely 0.05 kg was required for the treatment of a ton of nitrobenzene-containing water with pH from 3 to 11. The catalyzed Fe/Cu process is cost-effective and of practical value. PMID:18817068

Xu, Wenying; Li, Ping; Fan, Jinhong

2008-01-01

271

Components and coupling in enzyme-catalyzed reactions.  

PubMed

Many enzyme-catalyzed reactions involve coupling of two or more reactions that could otherwise be catalyzed separately. When biochemical reactions are coupled, the equilibrium composition is very different from that when the reactions are not coupled. The number of components in a chemical reaction is equal to the number of independent conservation equations for atoms of elements, but the number of components in an enzyme-catalyzed reaction that is coupled is larger than the number of independent conservation equations for atoms of elements. The investigation of these additional conservation equations by use of linear algebra is complicated by the fact that in dilute aqueous solutions, the activity of water is taken to be unity. This causes an incompatibility of conservation matrices and stoichiometric number matrices that can be avoided by use of the further transformed Gibbs energy G' ' that provides the criterion for spontaneous change and equilibrium when the standard transformed Gibbs energy of water is constant. In the most striking example discussed, the enzyme mechanism of a ligase reaction introduces three constraints in addition to conservation of atoms of elements. This is completely unheard of in chemical reaction thermodynamics. PMID:16851187

Alberty, Robert A

2005-02-10

272

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

ERIC Educational Resources Information Center

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

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

2011-01-01

273

Hematin- and peroxide-catalyzed peroxidation of phospholipid liposomes.  

PubMed

The effect of hydroperoxides on hematin-catalyzed initiation and propagation of lipid peroxidation was examined utilizing soybean phosphatidylcholine liposomes as model membranes. Polarographic and spectrophotometric methods revealed a bimodal pseudocatalytic activity for hematin. A slow initiation phase of peroxidation was observed in the presence of low peroxide concentrations, whereas a fast propagative phase was observed at higher peroxide levels. Peroxide levels were manipulated enzymatically by the combination of phospholipase A2 and lipoxidase or by the direct addition of linoleic acid hydroperoxide, cumene hydroperoxide, or hydrogen peroxide. In addition, the effect of two different techniques for liposome preparation, i.e., sonication and extrusion, were compared on the basis of peroxidation kinetics. High pressure liquid chromatography analysis showed that sonicated liposomes contained higher levels of endogenous peroxides than the extruded ones. These sonicated liposomes also exhibited more rapid peroxidation following hematin addition. Extruded liposomes were more resistant to hematin-catalyzed peroxidation but became better substrates when exogenous hydroperoxides were added. All three peroxides reacted with hematin during which decomposition of peroxide and irreversible oxidation of hematin took place. Spectral analysis of hematin indicated that a higher oxidation state of hematin iron may be transiently formed during reaction with hydroperoxides and accounts for the propagation of lipid peroxidation when reactions proceed in the presence of soybean phosphatidylcholine liposomes. Of the three peroxides studied, linoleic acid hydroperoxide was most efficient in supporting hematin-catalyzed lipid peroxidation. The relevance of our findings is discussed in terms of the concentration dependence for lipid peroxides in determining the rate and extent of radical propagation chain reactions catalyzed by heme-iron catalysts such as hematin. Variation of hematin and linoleic hydroperoxide concentrations may provide an efficient and reproducible method for inducing and manipulating the rates and extent of lipid peroxidation through facilitation of the propagative phase of lipid peroxidation. In addition, we address a problem inherent to in vitro studies of heme-catalyzed lipid peroxidation where preparations of peroxide-free membranes should be of concern. PMID:1898030

Kim, E H; Sevanian, A

1991-08-01

274

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

Microsoft Academic Search

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

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

2010-01-01

275

A Link between Protein Structure and Enzyme Catalyzed Hydrogen Tunneling  

NASA Astrophysics Data System (ADS)

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.

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

1997-11-01

276

Molecular mechanism of Ca(2+)-catalyzed fusion of phospholipid micelles.  

PubMed

Although membrane fusion plays key roles in intracellular trafficking, neurotransmitter release, and viral infection, its underlying molecular mechanism and its energy landscape are not well understood. In this study, we employed all-atom molecular dynamics simulations to investigate the fusion mechanism, catalyzed by Ca(2+) ions, of two highly hydrated 1-palmitoyl-2-oleoyl-sn-3-phosphoethanolamine (POPE) micelles. This simulation system mimics the small contact zone between two large vesicles at which the fusion is initiated. Our simulations revealed that Ca(2+) ions are capable of catalyzing the fusion of POPE micelles; in contrast, we did not observe close contact of the two micelles in the presence of only Na(+) or Mg(2+) ions. Determining the free energy landscape of fusion allowed us to characterize the underlying molecular mechanism. The Ca(2+) ions play a key role in catalyzing the micelle fusion in three aspects: creating a more-hydrophobic surface on the micelles, binding two micelles together, and enhancing the formation of the pre-stalk state. In contrast, Na(+) or Mg(2+) ions have relatively limited effects. Effective fusion proceeds through sequential formation of pre-stalk, stalk, hemifused-like, and fused states. The pre-stalk state is the state featuring lipid tails exposed to the inter-micellar space; its formation is the rate-limiting step. The stalk state is the state where a localized hydrophobic core is formed connecting two micelles; its formation occurs in conjunction with water expulsion from the inter-micellar space. This study provides insight into the molecular mechanism of fusion from the points of view of energetics, structure, and dynamics. PMID:23911761

Tsai, Hui-Hsu Gavin; Juang, Wei-Fu; Chang, Che-Ming; Hou, Tsai-Yi; Lee, Jian-Bin

2013-08-02

277

Thiocyanate catalyzes myeloperoxidase-initiated lipid oxidation in LDL.  

PubMed

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

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

2004-07-15

278

A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes  

SciTech Connect

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

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

2012-01-01

279

[Novel L-amino acid ligases catalyzing oligopeptide synthesis].  

PubMed

L-Amino acid ligase (EC 6.3.2.28) is a microbial enzyme catalyzing formation of an alpha-peptide bond from unprotected L-amino acids in an ATP-dependent manner. The YwfE protein from Bacillus subtilis 168 was the first reported L-amino acid ligase, and it synthesizes various dipeptides. Thereafter, several L-amino acid ligases were newly obtained by in silico analysis using the ATP-grasp motif. But these L-amino acid ligases synthesize only dipeptide and no longer peptide. A novel L-amino acid ligase capable of catalyzing oligopeptide synthesis is required to increase the variety of peptides. We have previously found a new member of L-amino acid ligase, RizA, from B. subtilis NBRC3134, a microorganism that produces the peptide-antibiotic rhizocticin. We newly found that a gene at approximately 9 kbp upstream of rizA encoded a novel L-amino acid ligase RizB. Recombinant RizB synthesized homo-oligomers of branched-chain amino acids consisting of 2 to 5 amino acids, and also synthesized various heteropeptides. RizB is the first reported L-amino acid ligase that catalyzes oligopeptide synthesis. In addition, we obtained L-amino acid ligases showing oligopeptide synthesis activities by in silico analysis using BLAST, which is a set of similarity search programs. These L-amino acid ligases showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacteria adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones. PMID:21048404

Kino, Kuniki

2010-11-01

280

Effects of oxalate on Fe-catalyzed photooxidation of dissolved sulfur dioxide in atmospheric water  

Microsoft Academic Search

Fe-catalyzed photochemical oxidation of dissolved sulfur dioxide (SO2), S(IV), in the presence of oxalate has been studied under the conditions typical for acidified atmospheric water. The Fe(III)-catalyzed oxidation of S(IV) is first order with respect to S(IV) concentration in the absence of oxalate. The presence of oxalate strongly inhibits Fe(III)-catalyzed S(IV) oxidation due to the formation of Fe(III)–oxalato complexes both

Yuegang Zuo; Jian Zhan

2005-01-01

281

Chloroperoxidase catalyzed oxidations in t-butyl alcohol\\/water mixtures  

Microsoft Academic Search

Chloroperoxidase catalyzed oxidations of sulfides and indoles were performed in t-butyl alcohol\\/water mixtures at ambient temperature. t-Butyl alcohol\\/water (50:50, v\\/v) proved to be a good solvent system for performing synthetic oxidations catalyzed by chloroperoxidase. The sulfoxidation of alkyl aryl sulfides and related compounds catalyzed by chloroperoxidase in t-butyl alcohol\\/water mixtures (50:50, v\\/v) was compared to the sulfoxidation in water. In

M. P. J. van Deurzen; I. J. Remkes; F. van Rantwijk; R. A. Sheldon

1997-01-01

282

The cobalt-catalyzed alternating copolymerization of epoxides and carbon monoxide: a novel approach to polyesters.  

PubMed

The metal-catalyzed synthesis of polyolefins, polyketones, and polycarbonates is well-known in academia and is already successfully applied in industrial processes. Still missing, however, is the metal-catalyzed synthesis of aliphatic polyesters, as one of the most important biodegradeable polymer families. We report here on the cobalt-catalyzed alternating copolymerization of propylene oxide and carbon monoxide, affording atactic and isotactic polyhydroxybutyrates (PHB). The postulated mechanism is supported by online ATR-IR analytics. PMID:12010031

Allmendinger, Markus; Eberhardt, Robert; Luinstra, Gerrit; Rieger, Bernhard

2002-05-22

283

Probing the regiospecificity of enzyme-catalyzed steroid glycosylation.  

PubMed

The potential of a uniquely permissive engineered glycosyltransferase (OleD ASP) as a catalyst for steroid glycosylation is highlighted. The ability of OleD ASP to glucosylate a range of cardenolides and bufadienolides was assessed using a rapid LC-UV/MS-SPE-NMR analytical platform. While a bias toward OleD-catalyzed C3 monoglucosylation was observed, subtle alterations of the steroidal architecture, in some cases, invoked diglucosylation or, in one case (digoxigenin), C12 glucosylation. This latter case represents the first, and highly efficient, synthesis of digoxigenin 12-O-?-D-glucoside. PMID:23075289

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

2012-10-18

284

Enantioselective aldol reactions catalyzed by chiral phosphine oxides.  

PubMed

The development of enantioselective aldol reactions catalyzed by chiral phosphine oxides is described. The aldol reactions presented herein do not require the prior preparation of the masked enol ethers from carbonyl compounds as aldol donors. The reactions proceed through a trichlorosilyl enol ether intermediate, formed in situ from carbonyl compounds, which then acts as the aldol donor. Phosphine oxides activate the trichlorosilyl enol ethers to afford the aldol adducts with high stereoselectivities. This procedure was used to realize a directed cross-aldol reaction between ketones and two types of double aldol reactions (a reaction at one/two ? position(s) of a carbonyl group) with high diastereo- and enantioselectivities. PMID:23828817

Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2013-07-04

285

The kinetics and mechanism of metal-catalyzed autoxidation  

Microsoft Academic Search

The autoxidation of organic compounds, RH, occurs by a radical-catalyzed chain reaction to give hydroperoxides, RO2H, as primary products. The initial rate is -d[O2]\\/dt = kp[RH] {ki[Cat]\\/kt}1\\/2, or in the presence of an inhibitor, (In), kp[RH](ki[Cat]\\/kI[In]), where kp is the chain propagation rate; ki[Cat], the rate of radical catalysis; kt chain termination rate; kI[In] rate of inhibitor action. As oxidation

W. A. Waters

1971-01-01

286

Exploring Transition Metal Catalyzed Reactions via AB Initio Reaction Pathways  

NASA Astrophysics Data System (ADS)

The study and prediction of chemical reactivity is one of the most influential contributions of quantum chemistry. A central concept in the theoretical treatment of chemical reactions is the reaction pathway, which can be quite difficult to integrate accurately and efficiently. This talk will outline our developments in the integration of these pathways on ab initio potential energy surfaces. We will also describe results from recent studies on the kinetics of transition metal catalyzed reactions, including the importance of vibrational coupling to the reaction coordinate and the role of this coupling in catalytic rate enhancement.

Hratchian, Hrant P.

2011-06-01

287

Rh(I)-Catalyzed Direct Arylation of Azines  

PubMed Central

The Rh(I)-catalyzed direct arylation of azines has been developed. Quinolines and 2-substituted pyridines couple with aryl bromides to efficiently afford ortho-arylated azine products using the commercially available and air stable catalyst [RhCl(CO)2]2. Electron-deficient and rich aromatic bromides couple in good yields, and hydroxyl, chloro, fluoro, trifluoromethyl, ether and ketone functionality are compatible with the reaction conditions. Aroyl chlorides also serve as effective azine coupling partners to give ortho-arylation products via a decarbonylation pathway.

Berman, Ashley M.; Bergman, Robert G.; Ellman, Jonathan A.

2011-01-01

288

Synthesis of Dihydrobenzofurans via Palladium-Catalyzed Heteroannulations  

SciTech Connect

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

Roman Vladimirovich Rozhkov

2004-12-19

289

Some thoughts on the muon catalyzed fusion reactor  

SciTech Connect

The design of the muon catalyzed fusion reactor is discussed. Some of the engineering challenges and critical research areas such as ..pi../sup -/ meson transport, beam entry single crystal window and coherent x-ray for stripping the muon from ..cap alpha.. particle, are considered. In order to reduce the tritium inventory and neutron wall loading, use of the laser technique for manipulating the d-t mixture is considered. The heterogeneous d-t mixture using the droplet or jet is discussed. 39 refs., 6 figs.

Takahashi, H.

1986-01-01

290

Base-Catalyzed Depolymerization of Lignin: Separation of Monomers  

SciTech Connect

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

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

2007-12-01

291

Palladium-catalyzed amination of aryl halides on solid support.  

PubMed

[reaction: see text] The first examples of the Pd(0)-catalyzed amination of aryl halides using Rink-resins as nitrogen source are described. Pd(2)dba(3)/BINAP/NaO-t-Bu was found to be the most efficient catalyst/base system, while a solvent mixture of dioxane and tert-butyl alcohol was shown to enhance the selectivity toward the desired monoarylation. Moderate to good yields and excellent purities of the amination products were found with electron-poor aryl halides, while electon-rich aryl halides failed to react under these conditions. PMID:12489962

Weigand, Klaus; Pelka, Sylvie

2002-12-26

292

Stereoselective Isoxazolidine Synthesis Via Copper-Catalyzed Alkene Aminooxygenation  

PubMed Central

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

Karyakarte, Shuklendu D.; Smith, Thomas P.

2012-01-01

293

Oxidation of alkynes by hydrogen peroxide catalyzed by methylrhenium trioxide  

SciTech Connect

The oxidation of alkynes with hydrogen peroxide is catalyzed by methylrhenium trioxide. The reactions can be rationalized by postulating that an oxirene intermediate is formed between a rhenium peroxide and the alkyne. Internal alkynes yield {alpha}-diketones and carboxylic acids, the latter from the complete cleavage of the triple bonds. Rearrangement products were observed only for aliphatic alkynes. Terminal alkynes gave carboxylic acids and their derivatives and {alpha}-keto acids as the major products, but their yields varied with the solvent used. 5 tabs.

Zhu, Zuolin; Espenson, J.H. [Ames Lab., IA (United States)

1995-12-01

294

Oxidation of polycyclic aromatic hydrocarbons catalyzed by soybean peroxidase  

Microsoft Academic Search

Soybean peroxidase (SBP) catalyzes the oxidation of a variety of polycyclic aromatic hydrocarbons (PAHs) in the presence of\\u000a water-miscible organic cosolvents, including acetonitrile, tetrahydrofuran, and dimethylformamide (DMF). Oxidation was optimal\\u000a at pH 2.0–2.5, with substantially lower reactivity at pH 1.5 as well as at pH > 3.0. Despite the low pH activity optimum,\\u000a SBP had an observed half-life of 120

Jennifer J. Kraus; Inmar Z. Munir; James P. McEldoon; Douglas S. Clark; Jonathan S. Dordick

1999-01-01

295

Directed nickel-catalyzed negishi cross coupling of alkyl aziridines.  

PubMed

Herein we report a nickel-catalyzed C-C bond-forming reaction between simple alkyl aziridines and organozinc reagents. This method represents the first catalytic cross-coupling reaction employing a nonallylic and nonbenzylic Csp(3)-N bond as an electrophile. Key to its success is the use of a new N-protecting group (cinsyl or Cn) bearing an electron-deficient olefin that directs oxidative addition and facilitates reductive elimination. Studies pertinent to elucidation of the mechanism of cross coupling are also presented. PMID:23961769

Nielsen, Daniel K; Huang, Chung-Yang Dennis; Doyle, Abigail G

2013-08-30

296

Kinetics of catalyzed organosolv processing of pine wood  

SciTech Connect

The main phenomena involved in pine wood processing with HCl-catalyzed acetic acid media (wood solubilization, delignification, degradation of both cellulose and hemicellulose, and generation of hemicellulosic sugars and furfural) were studied. The effects of both reaction time (in the range 0--180 min) and catalyst concentration (in the range 0.15--0.45%) on pulp yield, residual lignin, polysaccharide degradation, and hemicellulosic sugar generation were correlated by phenomenological kinetic models developed for the two operational temperatures considered (115 or 130 C). The models (based on pseudohomogeneous, first-order kinetics) provided a good interpretation of the experimental data.

Parajo, J.C.; Alonso, J.L.; Santos, V. [Univ. of Vigo, Orense (Spain). Dept. of Chemical Engineering

1995-12-01

297

Self-regulated pulsed nucleation in catalyzed nanowire growth  

NASA Astrophysics Data System (ADS)

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

Dubrovskii, V. G.

2013-05-01

298

Enzyme catalyzed electricity-driven water softening system.  

PubMed

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

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

2012-08-29

299

Aldose Reductase-catalyzed Reduction of Aldehyde Phospholipids  

PubMed Central

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

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

2012-01-01

300

An antibody-catalyzed bimolecular Diels-Alder reaction  

SciTech Connect

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

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

1990-09-26

301

Chloride-catalyzed corrosion of plutonium in glovebox atmospheres  

SciTech Connect

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

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

1998-04-01

302

Solution-solid-solid mechanism: superionic conductors catalyze nanowire growth.  

PubMed

The catalytic mechanism offers an efficient tool to produce crystalline semiconductor nanowires, in which the choice, state, and structure of catalysts are active research issues of much interest. Here we report a novel solution-solid-solid (SSS) mechanism for nanowire growth catalyzed by solid-phase superionic conductor nanocrystals in low-temperature solution. The preparation of Ag2Se-catalyzed ZnSe nanowires at 100-210 °C is exampled to elucidate the SSS model, which can be extendable to grow other II-VI semiconductor (e.g., CdSe, ZnS, and CdS) nanowires by the catalysis of nanoscale superionic-phase silver or copper(I) chalcogenides (Ag2Se, Ag2S, and Cu2S). The exceptional catalytic ability of these superionic conductors originates from their structure characteristics, known for high-density vacancies and fast mobility of silver or copper(I) cations in the rigid sublattice of Se(2-) or S(2-) ions. Insights into the SSS mechanism are provided based on the formation of solid solution and the solid-state ion diffusion/transport at solid-solid interface between catalyst and nanowire. PMID:23919513

Wang, Junli; Chen, Kangmin; Gong, Ming; Xu, Bin; Yang, Qing

2013-08-08

303

Triethylenetetramine prevents insulin aggregation and fragmentation during copper catalyzed oxidation.  

PubMed

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

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

2013-02-09

304

Water as an Activator for Palladium(II)-Catalyzed Olefin Polymerization.  

PubMed

By a reasonable combination of the Wacker reaction and olefin polymerization processes, water proves to be an excellent activator for the palladium(II)-catalyzed polymerization of ethylene and it provides a safe, environmental-friendly and handy initiator for olefin polymerization. The activity of the olefin polymerization is comparable to reactions catalyzed by the corresponding alkylated cationic palladium complexes. PMID:24038439

Tao, Wen-Jie; Li, Jun-Fang; Peng, Ai-Qing; Sun, Xiu-Li; Yang, Xiao-Hong; Tang, Yong

2013-09-03

305

Palladium-Catalyzed Intramolecular Carbopalladation/Cyclization Cascade: Access to Polycyclic N-Fused Heterocycles  

PubMed Central

An efficient palladium-catalyzed intramolecular carbopalladation/cyclization cascade toward tetra- and pentacyclic N-fused heterocycles has been developed. This transformation proceeds via the palladium-catalyzed coupling of aryl halides with internal propargylic esters or ethers followed by the 5-endo-dig cyclization leading to polycyclic pyrroloheterocycles in moderate to excellent yields.

Chernyak, Dmitri

2011-01-01

306

Pd-catalyzed cyclization and carbene migratory insertion: new approach to 3-vinylindoles and 3-vinylbenzofurans.  

PubMed

A Pd-catalyzed stereoselective synthesis of 3-vinylindoles and 3-vinylbenzofurans has been developed. The reaction merges the alkyne-based Pd-catalyzed cyclization and Pd carbene migratory insertion in a single catalytic cycle, generating a C-C single bond and a C?C double bond in one operation. PMID:24066705

Liu, Zhenxing; Xia, Ying; Zhou, Shiyi; Wang, Long; Zhang, Yan; Wang, Jianbo

2013-09-25

307

Lasalocid-catalyzed proton conductance in Streptococcus bovis as affected by extracellular potassium.  

PubMed Central

The effect of extracellular potassium on lasalocid-catalyzed proton conductance in Streptococcus bovis 24 was measured by using the fluorescent probe 9-aminoacridine. Increasing external potassium concentration resulted in decreased proton flux into S. bovis cells exposed to the ionophore. These results suggest that lasalocid catalyzes K+/H+ exchange diffusion in S. bovis cells.

Schwingel, W R; Bates, D B; Denham, S C; Beede, D K

1989-01-01

308

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

PubMed

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

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

2013-03-26

309

Regioselective bromohydroxylation of alkenes catalyzed by chloroperoxidase: Advantages of the immobilization of enzyme on talc  

Microsoft Academic Search

The bromohydroxylation of alkenes catalyzed by chloroperoxidase (CPO) from the mould Caldariomyces fumago adsorbed on different types of talc or in reverse micelles was compared to that of the same reaction catalyzed by the free enzyme in buffer. High reactivity was observed in all media, but the reaction was optimized with an enzyme-talc combination that produced the halohydrin with no

Salim Aoun; Michel Baboulène

1998-01-01

310

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

Microsoft Academic Search

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

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

2005-01-01

311

Nickel-catalyzed Arbuzov reactions of aryl triflates with triethyl phosphite  

Microsoft Academic Search

An efficient method was developed for the nickel-catalyzed phosphonylation of aryl triflates with triethyl phosphite, in which KBr as an additive promoted the SN2 catalytic step. To the best of our knowledge, this is the first example of nickel-catalyzed Arbuzov reactions of aryl triflates. Most of the substrates showed good reactivity under this catalytic system.

Guoqiang Yang; Chaoren Shen; Liang Zhang; Wanbin Zhang

2011-01-01

312

Synthesis of functionalized dioxa-aza[7]helicenes using palladium catalyzed arylations.  

PubMed

Despite the recent reports on transition-metal catalyzed cycloisomerization strategies toward helicenes, the amount of palladium catalyzed routes remains rather scarce. Within this letter the successful preparation and characterization of novel dioxa-aza[7]helicenes using palladium mediated coupling reactions is presented. PMID:22360768

Kelgtermans, Hans; Dobrza?ska, Liliana; Van Meervelt, Luc; Dehaen, Wim

2012-02-24

313

Divergent outcomes of gold(I)-catalyzed indole additions to 3,3-disubstituted cyclopropenes.  

PubMed

Depending on the conditions employed, gold(I)-catalyzed addition of indoles to 3,3-disubstituted cyclopropenes can be controlled to yield either 3-(E)-vinylindoles (3) or bis-indolylalkanes (4). If the cyclopropene substituents are sterically bulky, unprecedented gold-catalyzed oxidation under air occurs to yield bis-indolylalkene (5) and epoxide (6) at room temperature. PMID:22272604

Young, Paul C; Hadfield, Maximillian S; Arrowsmith, Lynn; Macleod, Kristina M; Mudd, Richard J; Jordan-Hore, James A; Lee, Ai-Lan

2012-01-24

314

Synthesis of Cocoa Butter Equivalent from Palm Oil by Carica papaya Lipase-Catalyzed Interesterification  

Microsoft Academic Search

Cocoa butter equivalent could be synthesized by lipase-catalyzed interesterification of oil. The objective of this research was to investigate the synthesis of cocoa butter equivalent from interesterification of palm oil catalyzed by Carica papaya lipase. The study showed that the compositions of cocoa butter equivalent were affected by acyl donor sources, substrate ratio, initial water of enzyme, reaction time, reaction

Porntippa Pinyaphong

2009-01-01

315

Total synthesis of (-)-kaitocephalin based on a Rh-catalyzed C-H amination.  

PubMed

A total synthesis of (-)-kaitocephalin, an ionotropic glutamate receptor antagonist, is accomplished in highly stereocontrolled manner via Overman rearrangement, rhodium-catalyzed benzylic C-H amination, pyrrolidine formation involving nucleophilic opening of a cyclic sulfamate, and rhodium-catalyzed allylic C-H amination as key steps. PMID:22390213

Takahashi, Keisuke; Yamaguchi, Daisuke; Ishihara, Jun; Hatakeyama, Susumi

2012-03-05

316

Ligand-free copper-catalyzed C-S coupling of aryl iodides and thiols.  

PubMed

A protocol for the copper-catalyzed aryl-sulfur bond formation between aryl iodides and thiophenols is reported. The reaction is catalyzed by a low amount (1-2.5 mol %) of readily available and ligand-free copper iodide salt. A variety of diaryl thioethers are synthesized under relatively mild reaction conditions with good chemoselectivity and functional group tolerance. PMID:18570479

Sperotto, Elena; van Klink, Gerard P M; de Vries, Johannes G; van Koten, Gerard

2008-06-21

317

Ligand-free copper-catalyzed C?S coupling of aryl iodides and thiols  

Microsoft Academic Search

A protocol for the copper-catalyzed aryl?sulfur bond formation between aryl iodides and thiophenols is reported. The reaction is catalyzed by a low amount (1?2.5 mol %) of readily available and ligand-free copper iodide salt. A variety of diaryl thioethers are synthesized under relatively mild reaction conditions with good chemoselectivity and functional group tolerance.

Elena Sperotto; Gerard P. M. van Klink; Johannes G. de Vries; Gerard van Koten

2008-01-01

318

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

319

Palladium-catalyzed synthesis of indoles via ammonia cross-coupling-alkyne cyclization.  

PubMed

The synthesis of indoles via the metal-catalyzed cross-coupling of ammonia is reported for the first time; the developed protocol also allows for the unprecedented use of methylamine or hydrazine as coupling partners. These Pd/Josiphos-catalyzed reactions proceed under relatively mild conditions for a range of 2-alkynylbromoarenes. PMID:21594239

Alsabeh, Pamela G; Lundgren, Rylan J; Longobardi, Lauren E; Stradiotto, Mark

2011-05-18

320

Gold-catalyzed cyclizations of alkynol-based compounds: synthesis of natural products and derivatives.  

PubMed

The last decade has witnessed dramatic growth in the number of reactions catalyzed by gold complexes because of their powerful soft Lewis acid nature. In particular, the gold-catalyzed activation of propargylic compounds has progressively emerged in recent years. Some of these gold-catalyzed reactions in alkynes have been optimized and show significant utility in organic synthesis. Thus, apart from significant methodology work, in the meantime gold-catalyzed cyclizations in alkynol derivatives have become an efficient tool in total synthesis. However, there is a lack of specific review articles covering the joined importance of both gold salts and alkynol-based compounds for the synthesis of natural products and derivatives. The aim of this Review is to survey the chemistry of alkynol derivatives under gold-catalyzed cyclization conditions and its utility in total synthesis, concentrating on the advances that have been made in the last decade, and in particular in the last quinquennium. PMID:22143545

Alcaide, Benito; Almendros, Pedro; Alonso, José M

2011-09-13

321

CuCl/bipyridine-catalyzed addition reactions of arylboroxines with aldehydes, ?,?-unsaturated ketones, and N-tosyl aldimines.  

PubMed

CuCl/bipyridine-catalyzed addition reactions of arylboroxines with aldehydes and ?,?-unsaturated ketones at elevated temperatures were described. By using the microwave energy, CuCl/bipyridine-catalyzed addition reactions of arylboroxines with aldimines were also realized. PMID:21827191

Liao, Yuan-Xi; Hu, Qiao-Sheng

2011-08-23

322

The palladium-catalyzed trifluoromethylation of aryl chlorides.  

PubMed

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

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

2010-06-25

323

Trypsin-catalyzed oxygen-18 labeling for quantitative proteomics  

SciTech Connect

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

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

2011-07-01

324

Homogeneously catalyzed oxidation for the destruction of aqueous organic wastes  

SciTech Connect

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

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

1990-11-01

325

Cobalt-catalyzed cross addition of silylacetylenes to internal alkynes.  

PubMed

A CoCl2·6H2O/Zn reagent using 2-(2,6-diisopropylphenyl)iminomethylpyridine (dipimp), 1,2-bis(diphenylphosphino)ethane (dppe), or 1,2-bis(diphenylphosphino)benzene (dppPh) as a ligand effectively catalyzed the cross-addition reaction of silylacetylene to internal alkynes. The reaction of some unsymmetrical internal alkynes, such as 3-arylpropargyl alcohols, proceeded in a highly regioselective manner in the presence of dppe or dppPh but gave a nearly 1:1 mixture of regioisomers in the presence of dipimp. The results of reactions using 1-deuterated 2-silylacetylene revealed that the reaction involves a direct oxidative addition of the silylacetylenic C-H bond to cobalt. PMID:23510302

Sakurada, Tetsuya; Sugiyama, Yu-ki; Okamoto, Sentaro

2013-04-01

326

Muonic molecule formation in muon-catalyzed fusion  

NASA Astrophysics Data System (ADS)

A negative muon induces nuclear-fusion reactions between hydrogen isotopes. In this reaction, a muon plays a role of a catalyst, i.e. muon injection causes a chain reaction of nuclear fusions in hydrogen system. This phenomenon is called muon catalyzed fusion or ?CF for short. A fusion reaction itself is dominated by nuclear force in the energy range of mega-electron-volt, however ?CF reaction is affected by much-low-energy phenomena like temperature and density in the range of milli-electron-volt. This is due to the muonic molecule formation through which a fusion reaction occurs. Therefore, ?CF has been an attractive subject for atomic physics as well as nuclear physics.

Kawamura, Naritoshi; Ishida, Katsuhiko; Matsuzaki, Teiichiro; Imao, Hiroshi; Nagamine, Kanetada

2010-04-01

327

Lipase-catalyzed synthesis of fattythioic acids from palm oil.  

PubMed

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

Al-Mulla, Emad A Jaffar

2011-01-01

328

Palladium-catalyzed dehydrostannylation of n-alkyltin trichlorides.  

PubMed

[Pd(PPh(3))(4)] catalyzes the dehydrostannylation of n-alkyltin trichlorides into HSnCl(3)(THF)(n) and isomers of the corresponding alkene. The reaction mechanism involves oxidative addition of the Sn-C bond followed by ?-H elimination from the resulting n-alkylpalladium trichlorostannyl species. Rate-determining reductive elimination of HSnCl(3) from cis-[PdH(SnCl(3))(PPh(3))(2)] completes the catalytic cycle. Organotin trichlorides without ?-H atoms either do not react or undergo thermal disproportionation. These results are relevant to understand some of the problems associated with the use of monoalkyltin compounds as coupling partner in Stille-type cross-coupling reactions as well as with the catalytic hydrostannylation of 1-alkenes to monoalkyltin trichlorides. PMID:21804998

Cabon, Yves; Gebbink, Robertus J M Klein; Deelman, Berth-Jan

2011-08-01

329

The Palladium-Catalyzed Trifluoromethylation of Aryl Chlorides  

PubMed Central

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.

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

2010-01-01

330

Novobiocin and coumermycin inhibit DNA supercoiling catalyzed by DNA gyrase.  

PubMed Central

Novobiocin and coumermycin are known to inhibit the replication of DNA iing of DNA catalyzed by E. coli DNA gyrase, a recently discovered enzyme that introduces negative superhelical turns into covalently circular DNA. The activity of DNA gyrase purified from a coumermycin-resistant mutant strain is resistant to both drugs. The inhibition by novobiocin of colicin E1 plasmid DNA replication in a cell-free system is partially relieved by adding resistant DNA gyrase. Both in the case of coliclls. DNA molecules which are converted to the covalently circular form in thepresence of coumermycin remain relaxed, instead of achieving their normal supercoiled conformation. We conclude that DNA gyrase controls the supercoiling of DNA in E. coli. Images

Gellert, M; O'Dea, M H; Itoh, T; Tomizawa, J

1976-01-01

331

Enantioselective cyclizations of silyloxyenynes catalyzed by cationic metal phosphine complexes.  

PubMed

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

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

2012-01-31

332

Experimental investigation of muon-catalyzed t + t fusion  

SciTech Connect

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

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

2009-02-15

333

Carbon dioxide reduction at a metal phthalocyanine catalyzed carbon electrode  

SciTech Connect

Metal phthalocyanines (metal = Co, Ni) deposited on carbon electrodes have been found to catalyze the electroreduction of carbon dioxide to formic acid in acid solutions (pH = 3-7). The overpotential for CO/sub 2/ reduction on cobalt phthalocyanine is approximately 200 mV lower than on the best metal cathodes at currents up to 10 mA/cm/sup 2/. The main reaction product in long-term electrolysis is the formate ion at pH>5. Methanol is also produced at lower pH values. The phthalocyanine becomes inactive in the less acid solutions once a fairly negative potential is imposed, probably due to an irreversible reduction of the catalyst.

Kapusta, S.; Hackerman, N.

1984-07-01

334

Mediator-assisted laccase-catalyzed oxidation of 4-hydroxybiphenyl.  

PubMed

The kinetics of oxidation of 4-hydroxybiphenyl (4-HBP) catalyzed by laccase from Polyporus pinsitus was studied in the presence of methyl syringate (MS), which acts as an electron-transfer mediator. Measurements were performed in 0.05 M acetate buffer, pH 5.5, in the presence of 4-HBP, MS, and laccase. It is shown that the oxidation rate of the lowly reactive substrate 4-HBP significantly increases during synergistic action of the highly reactive substrate MS. Bimolecular kinetic constants of interaction between the oxidized form of laccase and MS, the former and 4-HBP, and the oxidized form of MS and 4-HBP were calculated. A kinetic scheme of the synergistic substrate action is suggested; based on this scheme, the dependence of the initial rate on reagent concentration is derived. Analyzing experimental data, we obtained kinetic constants close to those obtained by modeling the processes. PMID:16732735

Bratkovskaya, I; Ivanec, R; Kulys, J

2006-05-01

335

Olefin hydroaryloxylation catalyzed by pincer-iridium complexes.  

PubMed

Aryl alkyl ethers, which are widely used throughout the chemical industry, are typically produced via the Williamson ether synthesis. Olefin hydroaryloxylation potentially offers a much more atom-economical alternative. Known acidic catalysts for hydroaryloxylation, however, afford very poor selectivity. We report the organometallic-catalyzed intermolecular hydroaryloxylation of unactivated olefins by iridium "pincer" complexes. These catalysts do not operate via the hidden Brønsted acid pathway common to previously developed transition-metal-based catalysts. The reaction is proposed to proceed via olefin insertion into an iridium-alkoxide bond, followed by rate-determining C-H reductive elimination to yield the ether product. The reaction is highly chemo- and regioselective and offers a new approach to the atom-economical synthesis of industrially important ethers and, potentially, a wide range of other oxygenates. PMID:24028199

Haibach, Michael C; Guan, Changjian; Wang, David Y; Li, Bo; Lease, Nicholas; Steffens, Andrew M; Krogh-Jespersen, Karsten; Goldman, Alan S

2013-09-27

336

Structural control of cytochrome P450-catalyzed ?-hydroxylation  

PubMed Central

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

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

2010-01-01

337

Transmembrane electron transfer catalyzed by phospholipid-linked manganese porphyrins  

SciTech Connect

Synthetic models can be very helpful in studying the effect of distance and orientation in electron transfer reactions in biological membrane processes such as occur in photosynthesis and mitochondria. To provide a model for the electron transfer where porphyrin pigments play the key role, the preparation of porphyrin derivatives that are capable of light-induced intra- or intermolecular electron transfer was reported. However, there has been little study of ground-state electron transfer between porphyrin complexes to provide insight into the effect of distance and orientation in the electron transfer so that a vectorial electron transfer system may be constructed in the biological membrane. We now report transmembrane electron transfer catalyzed by manganese complexes of bilayer-active phospholipid-linked porphyrins 1, PE-C{sub n}-MnTTP (n = 0, 5, 11) (Scheme I), which can be easily immersed into the lipid bilayer. The synthetic procedures leading are described.

Nango, Mamoru; Mizusawa, Atsushi; Miyake, Takenori; Yoshinaga, Junji (Univ. of Osaka Prefecture (Japan))

1990-02-14

338

Iridium-catalyzed intermolecular asymmetric hydroheteroarylation of bicycloalkenes.  

PubMed

Catalytic hydroarylation of alkenes is a desirable process because it can occur under neutral conditions with regioselectivity complementary to that of acid-catalyzed reactions and stereoselectivity derived from the catalyst. We report an intermolecular asymmetric addition of the C-H bonds of indoles, thiophenes, pyrroles, and furans to bicycloalkenes in high yield with high enantiomeric excess. These heteroarene alkylations occur ortho to the heteroatom. This selectivity is observed even with unprotected indoles, which typically undergo alkylation at the C3 position. Initial mechanistic studies revealed that oxidative addition of a heteroarene C-H bond to a neutral Ir(I) species occurs within minutes at room temperature and occurs in the catalytic cycle prior to the turnover-limiting step. Products from syn addition of the C-H bond across the olefin were observed. PMID:23346874

Sevov, Christo S; Hartwig, John F

2013-01-30

339

Specific miRNA Stabilization by Gld2-catalyzed Monoadenylation  

PubMed Central

miRNAs are small non-coding RNAs that inhibit translation and promote mRNA decay. The levels of mature miRNAs are the result of different rates of transcription, processing, and turnover. The non-canonical polymerase Gld2 has been implicated in the stabilization of miR-122 possibly by catalyzing 3? monoadenylation, however, there is little evidence that this relationship is one of cause and effect. Here, we biochemically characterize Gld2 involvement in miRNA monoadenylation and its effect on miRNA stability. We find that Gld2 directly monoadenylates and stabilizes specific miRNA populations in human fibroblasts and that sensitivity to monoadenylation-induced stability depends on nucleotides in the miRNA 3? end. These results establish a novel mechanism of miRNA stability and resulting post-transcriptional gene regulation.

D'Ambrogio, Andrea; Gu, Weifeng; Udagawa, Tsuyoshi; Mello, Craig C.; Richter, Joel D.

2012-01-01

340

Alkaline phosphatase-catalyzed silver deposition for electrochemical detection.  

PubMed

Alkaline phosphatase (AP) is one of the most used enzymatic labels for the development of ELISAs, immunosensors, DNA hybridization assays, etc. This enzyme catalyzes the dephosphorylation of a substrate into a detectable product usually quantified by optical or electrochemical measurements. This work is based on a substrate (3-indoxyl phosphate) that produces a compound able to reduce silver ions in solution into a metallic deposit, which is localized where the enzymatic label AP is attached. The deposited silver is electrochemically stripped into solution and measured by anodic stripping voltammetry. Its application to an enzymatic genosensor on streptavidin-modified screen-printed carbon electrodes for the detection of virulence nucleic acid determinants of autolysin gene, exclusively present on the genome of the human pathogen Streptococcus pneumoniae, is described. Compared with the direct voltammetric detection of indigo carmine, the anodic stripping voltammetry of silver ions is 14-fold more sensitive. PMID:17569504

Fanjul-Bolado, Pablo; Hernández-Santos, David; González-García, María Begoña; Costa-García, Agustín

2007-06-15

341

Effects of deferrioxamine on iron-catalyzed lipid peroxidation.  

PubMed

The kinetics of iron binding by deferrioxamine B mesylate and the ramifications of this process upon iron-catalyzed lipid peroxidation were assessed. The relative rates of Fe(III) binding by deferrioxamine varied for the chelators tested as follows: ADP greater than AMP greater than citrate greater than histidine greater than EDTA. The addition of a fivefold molar excess of deferrioxamine to that of Fe(III) did not result in complete binding (within 10 min) for any of the Fe(III) chelates tested except ADP:Fe(III). The rates of Fe(III) binding by deferrioxamine were greater at lower pH and when the competing chelator concentration was high in relationship to iron. The relatively slow binding of Fe(III) by deferrioxamine also affected lipid peroxidation, an iron-dependent process. The addition of deferrioxamine to an ascorbate- and ADP:Fe(III)-dependent lipid peroxidation system resulted in a time-dependent inhibition or stimulation of malondialdehyde formation (i.e., lipid peroxidation), depending on the ratio of deferrioxamine to iron. Converse to Fe(III), the rates of Fe(II) binding by deferrioxamine from the chelators tested above were rapid and complete (within 1 min), and resulted in the oxidation of Fe(II) to Fe(III). Lipid peroxidation dependent on Fe(II) autoxidation was stimulated by the addition of deferrioxamine. Malondialdehyde formation in this system was inhibited by the addition of catalase, and a similar extent of lipid peroxidation was achieved by substituting hydrogen peroxide for deferrioxamine. Collectively, these results suggest that the kinetics of Fe(III) binding by deferrioxamine is a slow, variable process, whereas Fe(II) binding is considerably faster. The binding of either valence of iron by deferrioxamine may result in variable effects on iron-catalyzed processes, such as lipid peroxidation, either via slow binding of Fe(III) or the rapid binding of Fe(II) with concomitant Fe(II) oxidation. PMID:1586153

Miller, D M; Spear, N H; Aust, S D

1992-06-01

342

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

PubMed

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

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

2009-09-15

343

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

PubMed Central

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

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

2011-01-01

344

Electrochemical investigations into kinase-catalyzed transformations of tau protein.  

PubMed

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

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

2013-05-20

345

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

SciTech Connect

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

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

2008-07-29

346

High power density yeast catalyzed microbial fuel cells  

NASA Astrophysics Data System (ADS)

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

Ganguli, Rahul

347

Theoretical studies of iron(iii)-catalyzed intramolecular C-H amination of azides.  

PubMed

Density functional theory calculations have been carried out to study the reaction mechanism of the [Fe(III)(F20TPP)Cl] catalyzed C-H amination reaction. The calculations show that the classical three-step mechanism for other metals (Ru, Rh, Ir and Zn), including N2 liberation, C-N bond formation and 1,2-hydrogen shift, does not fit the iron(iii)-catalyzed system. After N2 liberation, the favorable reaction pathway for the iron(iii)-catalyzed system is a 1,2-hydrogen shift preceding C-N bond formation, i.e., a H-abstraction/radical rebound mechanism. PMID:24005880

Li, Juan; Wu, Caihong; Zhang, Qi; Yan, Bo

2013-09-24

348

beta-D-Galactosidase from Paenibacillus thiaminolyticus catalyzing transfucosylation reactions.  

PubMed

A genomic library of bacterial strain Paenibacillus thiaminolyticus was constructed and the plasmid DNA of the clone, containing the gene encoding beta-d-galactosidase with beta-d-fucosidase activity, detected by 5-bromo-4-chloro-3-indoxyl beta-d-galactopyranoside, was sequenced. Cells of Escherichia coli BL21 (DE3) were used for production of the enzyme in the form of a histidine-tagged protein. This recombinant fusion protein was purified using Ni-NTA agarose affinity chromatography and characterized by using p-nitrophenyl beta-d-fucopyranoside (K(m) value of (1.18 +/- 0.06) mmol/L), p-nitrophenyl beta-d-galactopyranoside (K(m) value of (250 +/- 40) mmol/L), p-nitrophenyl beta-d-glucopyranoside (K(m) value of (77 +/- 6) mmol/L), and lactose (K(m) value of (206 +/- 5) mmol/L) as substrates. Optimal pH and temperature were estimated as 5.5 and 65 degrees C, respectively. According to the amino acid sequence, the molecular weight of the fusion protein was calculated to be 68.6 kDa and gel filtration chromatography confirmed the presence of the enzyme in a monomeric form. In the following step, its ability to catalyze transfucosylation reactions was tested. The enzyme was able to catalyze the transfer of fucosyl moiety to different p-nitrophenyl glycopyranosides (producing p-nitrophenyl beta-d-fucopyranosyl-(1,3)-beta-d-fucopyranoside, p-nitrophenyl beta-d-fucopyranosyl-(1,3)-alpha-d-glucopyranoside, p-nitrophenyl beta-d-fucopyranosyl-(1,3)-alpha-d-mannopyranoside, and p-nitrophenyl beta-d-fucopyranosyl-(1,6)-alpha-d-galactopyranoside) and alcohols (producing methyl beta-d-fucopyranoside, ethyl beta-d-fucopyranoside, 1-propyl beta-d-fucopyranoside, 2-propyl beta-d-fucopyranoside, 1-octyl beta-d-fucopyranoside, and 2-octyl beta-d-fucopyranoside). These results indicate the possibility of utilizing this enzyme as a promising tool for enzymatic synthesis of beta-d-fucosylated molecules. PMID:20008517

Benesová, Eva; Lipovová, Petra; Dvoráková, Hana; Králová, Blanka

2009-12-14

349

Coupling of iodotyrosine catalyzed by human thyroid peroxidase in vitro.  

PubMed

The coupling of iodotyrosine (coupling reaction) is one of the least studied in the formation of thyroid hormone, particularly in human thyroid diseases. This paper describes a method of measuring iodotyrosine coupling catalyzed by human thyroid peroxidase (TPO) in vitro. There were two important requirements to demonstrate the coupling reaction: 1) thyroglobulin with a low thyroid hormone content, and 2) partially purified TPO. Thyroglobulin with low thyroid hormone content was obtained from Grave's and follicular adenoma tissues after propylthiouracil (PTU) therapy and L-T4 therapy, respectively. TPO was prepared from Graves' thyroid by solubilizing the 100,000 X g pellet of thyroid homogenate with sodium deoxycholate and trypsin, followed by Sephacryl S-300 gel filtration. Before the coupling reaction, thyroglobulin was iodinated with chloramine-T and potassium iodide, followed by dialysis. The coupling reaction was carried out by incubating newly iodinated thyroglobulin with TPO, diiodotyrosine, a coupling stimulator, and a H2O2-generating system (glucose and glucose oxidase) for 20 min at 37 C. After thyroglobulin was digested with Pronase, the thyroid hormone content of the thyroid digest was measured by RIA. Coupling activity was measured by the amount of newly formed T3 (nanograms of T3 per mg thyroglobulin). The time course of coupling reaction showed a progressive increase in coupling activity up to 30 min, and the reaction was temperature and pH dependent, with a pH optimum of 7.0. Coupling activity in the presence of H2O2 and TPO was 43 +/- 5.0 ng T3/mg thyroglobulin (mean +/- SD of triplicate samples), and addition of diiodotyrosine to the H2O2-TPO system caused a nearly 3-fold increase in coupling activity. This method has potential utilization for measurement of peroxidase coupling activity, since there was a linear relationship between the measured coupling activity and the amount of added TPO when the TPO concentration was over 3 micrograms/300 microliter. Methimazole (MMI) and PTU had similar potencies in inhibiting the TPO-catalyzed coupling reaction, whereas MMI was distinctly more potent than PTU as an inhibitor of TPO-mediated iodination in vitro. The different potencies of MMI in the two reactions suggest that different inhibitory mechanisms may be involved in iodination and coupling. The reducing agent, sodium metabisulfite, was also found to be a more potent inhibitor of the TPO-mediated coupling reaction than of the TPO-mediated iodination reaction. The method of iodotyrosine coupling described here may be useful to investigate the coupling step of thyroid hormone formation in human thyroid diseases. PMID:3838997

Sugawara, M

1985-06-01

350

Coalification by clay-catalyzed oligomerization of plant monomers. [Methylisoeugenol  

SciTech Connect

During this reporting period, we have obtained a model of montmorillonite clay, and this model has been of great assistance in visualizing how the chemistry of substrate molecules might be altered as it occurs on the surface of the clay. A stereochemical representation of this montmorillonite model is shown. In our previous report, we indicated that the dimerization of methylisoeugenol with the montmorillonite clay K-10 afforded a variety of indanes and indenes which were formed via acid-catalyzed processes. In addition, we have now observed a pair of naphthalene isomers. This observation lends strong support to the hypothesis that radical cation Diels-Alder dimerizations occur on the surface of the montmorillonite clay K-10. Furthermore, when the dimerization is conducted in homogeneous media, only two indanes are formed. However, when this same dimerization is conducted on the surface of K-10, six indanes are produced. Based upon these considerations, the distribution of indane isomers might indicate that dimerization is taking place both in the homogeneous medium surrounding the clay and on the surface of the clay. Samples of K-10 were pretreated with DBU, dicyclohexylamine, triphenylamine, and triton-B. The pretreatments completely inhibited indane formation. In addition, the partially neutralization of K-10 by the pretreatment with finely ground Na{sub 2}CO{sub 3} was attempted. This procedure did not alter the ratios of indanes products from those observed with the untreated K-10.

Orchin, M.; Wilson, R.M.

1989-01-01

351

Histone catalyzed cleavage of nucleosomal DNA containing 2-deoxyribonolactone  

PubMed Central

Oxidized abasic sites such as 2-deoxyribonolactone (L) are produced in DNA by a variety of oxidizing agents, including potent cytotoxic antitumor natural products. 2-Deoxyribonolactone is labile to alkaline conditions but its half-life in free DNA at pH 7.5 is approximately one week. Independent generation of L at defined positions within nucleosomes reveals that the histone proteins catalyze strand scission and increase the rate between 11 and ?43-fold. Mechanistic studies indicate that DNA-protein cross-links are not intermediates en route to strand scission and that C2-deprotonation is the rate determining step. The use of mutant histone H4 proteins demonstrates that the lysine rich tail that is often post-translationally modified in cells contributes to the cleavage of L but is not the sole source of the enhanced cleavage rates. Consideration of DNA repair in cells suggests that L formation in nucleosomal DNA as part of bistranded lesions by antitumor antibiotics results in de facto double strand breaks, the most deleterious form of DNA damage.

Zhou, Chuanzheng; Greenberg, Marc M.

2012-01-01

352

Transition metal-catalyzed carbon-carbon bond activation.  

PubMed

This tutorial review deals with recent developments in the activation of C-C bonds in organic molecules that have been catalyzed by transition metal complexes. Many chemists have devised a variety of strategies for C-C bond activation and significant progress has been made in this field over the past few decades. However, there remain only a few examples of the catalytic activation of C-C bonds, in spite of the potential use in organic synthesis, and most of the previously published reviews have dwelt mainly on the stoichiometric reactions. Consequently, this review will focus mainly on the catalytic reaction of C-C bond cleavage by homogeneous transition metal catalysts. The contents include cleavage of C-C bonds in strained and unstrained molecules, and cleavage of multiple C-C bonds such as C[triple bond]C triple bonds in alkynes. Multiple bond metathesis and heterogeneous systems are beyond the scope of this review, though they are also fascinating areas of C-C bond activation. In this review, the strategies and tactics for C-C bond activation will be explained. PMID:15592626

Jun, Chul-Ho

2004-11-04

353

Tin(IV) catalyzed D-galacturonic acid anomerization.  

PubMed

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

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

2007-11-23

354

The platinum-catalyzed oxidation of 2-propanol  

SciTech Connect

The platinum-catalyzed oxidation of 2-propanol was run over a series of single-turnover (STO) characterized Pt/CPG (Controlled Pore Glass) catalysts. Comparison of reaction rates with STO site densities showed that the oxidation was taking place on the more coordinatively unsaturated corner atoms on the catalysts. Specific site TOFs were found to be 5.5, 7.9, and 5.0 moles O[sub 2] uptake/mole of site/min for the [sup 3]M[sub 1], [sup 3]M[sub R], and [sup 3]MH sites, respectively. Initial rate data were obtained for reactions run at several 2-propanol concentrations at three separate oxygen pressures. These data were analyzed using the double reciprocal Lineweaver-Burke method commonly employed in enzyme kinetic determinations. The data obtained showed that oxygen was adsorbed about 200 times more strongly than 2-propanol in these reactions. A maximum rate value of 18 moles O[sub 2] consumed/mole of active site/min was calculated. This value represents the maximum rate for the reaction when it is run under zero-order conditions for both reactants without diffusion limitations. The present data were obtained, however, under first order reaction conditions. Given the difference in reaction conditions, the experimentally determined TOF of 6 min[sup [minus]1] is not an unreasonable value. 49 refs., 9 figs., 3 tabs.

Augustine, R.L.; Doyle, L.K. (Seton Hall Univ., South Orange, NJ (United States))

1993-05-01

355

Kinetic modeling of Pt-catalyzed glycolaldehyde decomposition to syngas.  

PubMed

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

Salciccioli, Michael; Vlachos, Dionisios G

2012-04-26

356

Temperature dependences of rate coefficients for electron catalyzed mutual neutralization  

SciTech Connect

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

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

2011-07-14

357

Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide  

NASA Astrophysics Data System (ADS)

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

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

2003-07-01

358

Iron oxide surface catalyzed oxidation of quinoline by hydrogen peroxide  

SciTech Connect

The objective of this research was to examine and compare the surface catalyzed loss of quinoline, a model pollutant, in the presence of three iron oxides: ferrihydrite, goethite, and a semicrystalline iron oxide. These are ubiquitous in the subsurface environment and have been implicated in the possible abiotic loss of contaminants when hydrogen peroxide is injected for augmenting bioremediation. This suggests the possible use of hydrogen peroxide specifically as an oxidant of some compounds in the subsurface. A comparison also reveals the best candidate for use in a supported oxide fixed bed treatment system utilizing hydrogen peroxide as an oxidant. The catalytic activity toward quinoline oxidation was highest for goethite, much less for the semicrystalline material, and negligible in the presence of ferrihydrite. Several water constituents affected reaction rates and stoichiometry by adsorption or through effects on solution chemistry. The stoichiometric efficiency relating quinoline loss to hydrogen peroxide decomposition was not a function of oxide concentration, nor was it affected by the presence of carbonate or phosphate that reduced the rate of hydrogen peroxide decomposition. The effect of humic acid on quinoline loss and hydrogen peroxide decomposition rate depended on its concentration, suggesting that it may act as a radical scavenger, radical chain promoter, and catalytic site inhibitor.

Valentine, R.L.; Wang, H.C.A. [Univ. of Iowa, Iowa City, IA (United States). Dept. of Civil and Environmental Engineering

1998-01-01

359

Primordial lithium abundance in catalyzed big bang nucleosynthesis  

SciTech Connect

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.

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

360

Clay-catalyzed reactions of coagulant polymers during water chlorination  

USGS Publications Warehouse

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

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

2004-01-01

361

Studies on the catalyzed interconversions of vitamin A derivatives  

SciTech Connect

The kinetics of I/sub 2/-catalyzed isomerization of the retinal isomers were studied. The all-trans isomer formed 13-cis-retinal rapidly with a rate constant of 1.9 X 10/sup -4/ s/sup -1/. The reverse reaction occurred with a rate constant of 4.5 X 10/sup -4/ s/sup -1/. The 11-cis isomer was first converted to all-trans-retinal with a rate constant of 3.1 X 10/sup -4/ s/sup -1/, although the 13-cis isomer was also rapidly formed. The 9-cis isomer was isomerized to the 9-cis, 13-cis isomer before the other isomers were generated and the 13-cis isomer was converted to its all-trans congener prior to the formation of the other isomers. Similar results appear to occur when other methods of catalysis are used. This isomerization about the C/sub 13/-C/sub 14/ doubled bond appears to be a kinetically favored event, eliminating the possibility that 11-cis might be a kinetic product formed from the all-trans isomer. At equilibrium, only 0.1% of 11-cis-retinal is found. Equilibration of all-trans-retinol palmitate also generated very little of the 11-cis isomer (less than or equal to0.2%) 11-cis-retinol palmitate at equilibrium. The implications of these results for an 11-cis-retinal regeneration mechanism in the eye are discussed.

Rando, R.R.; Chang, A.

1983-05-04

362

Dephenolization of industrial wastewaters catalyzed by polyphenol oxidase  

SciTech Connect

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

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

1984-01-01

363

ATP-Independent Hydrocarbon Formation Catalyzed by Isolated Nitrogenase Cofactors  

PubMed Central

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

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

2012-01-01

364

Helium Catalyzed D-D Fusion in a Levitated Dipole  

NASA Astrophysics Data System (ADS)

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

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

2003-10-01

365

Catalyzed isomerization and decarbonylation of ionized formic acid and dihydroxycarbene  

NASA Astrophysics Data System (ADS)

Catalyzed conversion of HCOOH[radical sign]+ into HOCOH[radical sign]+ was studied in the cell of a FT-ICR in the presence of different molecules. The reaction of HCOOH[radical sign]+ with SO2, whose proton affinity (PA) lies between that of the HOCO[radical sign] radical at the carbon and at the oxygen sites, yields the HOCOH[radical sign]+ carbene isomer as proved by its characteristic reaction with cyclopropane. When the PA of the catalyst lies above the highest PA of both sites of the HOCO[radical sign] radical, formation of HOCOH[radical sign]+ cannot be observed since its final state lies above that corresponding to protonation of the catalyst. However, reactions of DCO2H[radical sign]+ and of HCO2D[radical sign]+, which protonate several catalysts in an identical ratio which is very near of 1/1 at the beginning of the reaction, indicates that both ions, DCO2H[radical sign]+ and of HCO2D[radical sign]+, convert into ion DO-C-OH[radical sign]+ within a complex prior to protonation. The reactions of HCOOH[radical sign]+ and HOCOH[radical sign]+ with water were also more particularly studied by using theoretical calculations. Both reactions lead to protonated water and to the ionized water dimer which has been shown to possess the [H2OH+...OH[radical sign

Rest, Guillaume Van Der; Mourgues, Philippe; Audier, Henri E.

2004-01-01

366

Ab initio study of ice catalyzation of HOCl + HCl reaction  

SciTech Connect

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.

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

2000-06-15

367

Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation of Enol Carbonates  

PubMed Central

Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio- and enantio-selective process for the synthesis of ketones bearing either a quaternary or a tertiary ?-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic di-substituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium enolates, the DAAA reaction proceeds through an “outer sphere” SN2 type of attack on the ?-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the ?-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of enolates associated with the equilibrium between different enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal enolates.

Trost, Barry M.; Xu, Jiayi; Schmidt, Thomas

2009-01-01

368

Iodide-Catalyzed Ozonation of ?-Pinene on Aqueous Surfaces  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

369

Iodide-catalyzed ozonation of terpenes on aqueous surfaces  

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

370

Broadening the scope of glycosyltransferase-catalyzed sugar nucleotide synthesis.  

PubMed

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

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

2013-04-22

371

Kinetics of phenolic polymerization catalyzed by peroxidase in organic media  

SciTech Connect

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

Xu, Y.P.; Huang, G.L; Yu, Y.T. [Nankai Univ., Tianjin (China). Inst. for Molecular Biology

1995-07-05

372

Process Intensification in Base-Catalyzed Biodiesel Production  

SciTech Connect

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.

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

2008-01-01

373

Production of Chemoenzymatic Catalyzed Monoepoxide Biolubricant: Optimization and Physicochemical Characteristics  

PubMed Central

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

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

2012-01-01

374

Rhodium-catalyzed cycloisomerization of N-propargyl enamine derivatives.  

PubMed

A novel rhodium-catalyzed cycloisomerization has been developed which converts N-propargyl enamine derivatives to their isomeric six-membered azacycles in good yields under mild reaction conditions. The [Rh(C2H2)2Cl]2/P(4-F-C6H4)3 catalyst, in combination with DABCO as a base and DMF as a solvent, was found to be effective in promoting the cyclization process. The reaction is proposed to proceed through an intramolecular nucleophilic attack of the enamine to the rhodium vinylidene followed by a base-mediated proton-shunting process. The base was found to play a crucial role in the transformation, indicating the proton migration to be an integral component of the catalytic cycle. An aprotic polar solvent was required for high conversion, which points to the intermediacy of a zwitterionic intermediate. The present reaction should prove useful for the efficient synthesis of various six-membered azacycles that are important structural motifs of many natural isolates and medicinal agents. PMID:16683796

Kim, Hahn; Lee, Chulbom

2006-05-17

375

Stereoselective palladium-catalyzed O-glycosylation using glycals.  

PubMed

A highly stereoselective palladium-catalyzed O-glycosylation reaction is described. The reaction of a glycal 3-acetate or carbonate with the zinc(II) alkoxide of acceptors establishes the glycosidic linkage under palladium catalysis to give rise to disaccharides as the product in good yields and with high stereoselectivity. In contrast to the Lewis acid mediated Ferrier procedure, the anomeric stereochemistry of this reaction is controlled by the employed ligand. Whereas the use of a complex of palladium acetate and 2-di(tert-butyl)phosphinobiphenyl as the catalyst results in the exclusive beta-glycoside formation, the same reaction using trimethyl phosphite ligand furnishes an alpha-anomer as the major product. The utility of the 2,3-unsaturation present in the resulting glycoside is demonstrated by the further transformations such as dihydroxylation, hydration, and hydrogenation reactions. Thus, the combination of the glycosylation and subsequent functionalization provides a novel entry to saccharides which are otherwise difficult to prepare. The broad scope of the process, mildness of the reaction conditions, and experimental simplicity should make this method a useful tool in synthetic carbohydrate chemistry. PMID:14759180

Kim, Hahn; Men, Hongbin; Lee, Chulbom

2004-02-11

376

Trinucleotide repeat expansions catalyzed by human cell-free extracts.  

PubMed

Trinucleotide repeat expansions cause 17 heritable human neurological disorders. In some diseases, somatic expansions occur in non-proliferating tissues such as brain where DNA replication is limited. This finding stimulated significant interest in replication-independent expansion mechanisms. Aberrant DNA repair is a likely source, based in part on mouse studies showing that somatic expansions are provoked by the DNA repair protein MutS? (Msh2-Msh3 complex). Biochemical studies to date used cell-free extracts or purified DNA repair proteins to yield partial reactions at triplet repeats. The findings included expansions on one strand but not the other, or processing of DNA hairpin structures thought to be important intermediates in the expansion process. However, it has been difficult to recapitulate complete expansions in vitro, and the biochemical role of MutS? remains controversial. Here, we use a novel in vitro assay to show that human cell-free extracts catalyze expansions and contractions of trinucleotide repeats without the requirement for DNA replication. The extract promotes a size range of expansions that is similar to certain diseases, and triplet repeat length and sequence govern expansions in vitro as in vivo. MutS? stimulates expansions in the extract, consistent with aberrant repair of endogenous DNA damage as a source of expansions. Overall, this biochemical system retains the key characteristics of somatic expansions in humans and mice, suggesting that this important mutagenic process can be restored in the test tube. PMID:23337586

Stevens, Jennifer R; Lahue, Elaine E; Li, Guo-Min; Lahue, Robert S

2013-01-22

377

Enzymatic polymerization catalyzed by immobilized endoglucanase on gold.  

PubMed

Enzymatic polymerization was carried out on gold by immobilized genetically engineered endoglucanase II (EGII) from Trichoderma viride , and the polymerization behavior and the produced cellulose were analyzed in comparison with those by free enzymes. Mutant EGIIs were EGII(core2) and EGII(core2H), which consist of two sequential catalytic core domains with one His-tag (His6) on N-terminal and with totally two His-tags on both terminals, respectively. His-tagged EGIIs were immobilized via Ni chelators of nitrilotriacetic acid (NTA) introduced on gold surface. From SPR measurements, the affinity of EGII(core2H) to the surface was higher than that of EGII(core2), and the molecular occupation area of EGII(core2H) was larger than that of EGII(core2), indicating that EGII(core2H) was immobilized with utilizing two His-tags introduced on both terminals. The hydrolytic activity of the immobilized EGII(core2H) using cellohexaose as substrate was slightly lower than that of free EGII(core2H) when they were compared at the same amount in the hydrolytic system. Enzymatic polymerization catalyzed by both immobilized EGII(core2) and EGII(core2H) proceeded with producing highly crystalline cellulose in comparison with free enzyme. Immobilization of the endoglucanase is thus effective to obtain crystalline cellulose due to the high density of the catalytic domain on gold. PMID:21261301

Nakamura, Itsuko; Horikawa, Yoshiki; Makino, Akira; Sugiyama, Junji; Kimura, Shunsaku

2011-01-24

378

Carbon-catalyzed gasification of organic feedstocks in supercritical water  

SciTech Connect

Spruce wood charcoal, macadamia shell charcoal, coal activated carbon, and coconut shell activated carbon catalyze the gasification of organic compounds in supercritical water. Feedstocks studied in this paper include glycerol, glucose, cellobiose, whole biomass feedstocks (depithed bagasse liquid extract and sewage sludge), and representative Department of Defense (DoD) wastes (methanol, methyl ethyl ketone, ethylene glycol, acetic acid, and phenol). The effects of temperature, pressure, reactant concentration, weight hourly space velocity, and the type of catalyst on the gasification of glucose are reported. Complete conversion of glucose (22% by weight in water) to a hydrogen-rich synthesis gas was realized at a weight hourly space velocity (WHSV) of 22.2 h{sup {minus}1} in supercritical water at 600 C, 34.5 MPa. Complete conversions of the whole biomass feeds were also achieved at the same temperature and pressure. The destruction efficiencies for the representative DoD wastes were also high. Deactivation of the carbon catalyst was observed after 4 h of operation without swirl in the entrance region of the reactor, but the carbon gasification efficiency remained near 100% for more than 6 h when a swirl generator was employed in the entrance of the reactor.

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

1996-08-01

379

Flavoenzymes catalyzing oxidative aromatic ring-cleavage reactions.  

PubMed

2-Methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) oxygenase (MHPCO) and 5-pyridoxic acid oxygenase are flavoenzymes catalyzing an aromatic hydroxylation and a ring-cleavage reaction. Both enzymes are involved in biodegradation of vitamin B6 in bacteria. Oxygen-tracer experiments have shown that the enzymes are monooxygnases since only one atom of molecular oxygen is incorporated into the products. Kinetics of MHPCO has shown that the enzyme is similar to single-component flavoprotein hydroxylases in that the binding of MHPC is required prior to the flavin reduction by NADH, and C4a-hydroperoxy-FAD and C4a-hydroxy-FAD are found as intermediates. Investigation on the protonation status of the substrate upon binding to the enzyme has shown that only the tri-ionic form of MHPC is bound at the MHPCO active site. Using a series of FAD analogues with substituents at the 8-position of the isoalloxazine ring, the oxygenation of MHPC by the C4a-hydroperoxy-FAD was shown to occur via an electrophilic aromatic substitution mechanism. Recently, the X-ray structures of MHPCO and a complex of MHPC-MHPCO at 2.1A have been reported and show the presence of nine water molecules in the enzyme active site. Based on structural data, a few residues, Tyr82, Tyr223, Arg181, were suggested to be important for catalysis of MHPCO. PMID:19728986

Chaiyen, Pimchai

2009-09-01

380

Investigations of Surface-Catalyzed Reactions in a Mars Mixture  

NASA Astrophysics Data System (ADS)

In the design of a thermal protection system (TPS) for a planetary entry vehicle, accurate modeling of the trajectory aero-heating poses a significant challenge owing to large uncertainties in chemical processes taking place at the surface. Even for surface-catalyzed reactions, which have been investigated extensively, there is no consensus on how they should be modeled; or, in some cases, on which reactions are likely to occur. Current TPS designs for Mars missions rely on a super-catalytic boundary condition, which assumes that all dissociated species recombine to the free stream composition.While this is recognized to be the the most conservative approach, discrepancies in aero-heating measurements in ground test facilities preclude less conservative design options, resulting in an increased TPS mass at the expense of scientific payload.Using two-photon absorption laser induced fluorescence in a 30 kW inductively coupled plasma torch facility, preliminary studies have been performed to obtain spatially-resolved measurements of the dominant species in a plasma boundary layer for a Martian atmosphere mixture over catalytic and non-catalytic surfaces.

Dougherty, M.; Owens, W.; Meyers, J.; Fletcher, D. G.

2011-08-01

381

Iron-catalyzed hydrogen production from formic acid.  

PubMed

Hydrogen represents a clean energy source, which can be efficiently used in fuel cells generating electricity with water as the only byproduct. However, hydrogen generation from renewables under mild conditions and efficient hydrogen storage in a safe and reversible manner constitute important challenges. In this respect formic acid (HCO(2)H) represents a convenient hydrogen storage material, because it is one of the major products from biomass and can undergo selective decomposition to hydrogen and carbon dioxide in the presence of suitable catalysts. Here, the first light-driven iron-based catalytic system for hydrogen generation from formic acid is reported. By application of a catalyst formed in situ from inexpensive Fe(3)(CO)(12), 2,2':6'2''-terpyridine or 1,10-phenanthroline, and triphenylphosphine, hydrogen generation is possible under visible light irradiation and ambient temperature. Depending on the kind of N-ligands significant catalyst turnover numbers (>100) and turnover frequencies (up to 200 h(-1)) are observed, which are the highest known to date for nonprecious metal catalyzed hydrogen generation from formic acid. NMR, IR studies, and DFT calculations of iron complexes, which are formed under reaction conditions, confirm that PPh(3) plays an active role in the catalytic cycle and that N-ligands enhance the stability of the system. It is shown that the reaction mechanism includes iron hydride species which are generated exclusively under irradiation with visible light. PMID:20550131

Boddien, Albert; Loges, Björn; Gärtner, Felix; Torborg, Christian; Fumino, Koichi; Junge, Henrik; Ludwig, Ralf; Beller, Matthias

2010-07-01

382

Reductive dechlorination catalyzed by bacterial transition-metal coenzymes  

SciTech Connect

The bacterial transition-metal coenzymes vitamin B{sub 12} (Co), coenzyme F{sub 430} (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 B{sub 12} and coenzyme F{sub 430}, reductive dechlorination rates for different classes of perchlorinated compounds had the following order: carbon tetrachloride > tetrachloroethylene > hexachlorobenzene. For hematin, the order of reductive dechlorination rates was carbon tetrachloride > hexachlorobenzene > tetrachloroethylene. Within each class of compounds, rates of dechlorination decreased with decreasing chlorine content. Regio- and stereospecificity were observed in these reactions. In the reductive dechlorination of trichloroethylene, cis-1,2-dichloroethylene was the predominant product formed with vitamin B{sub 12}, coenzyme F{sub 430}, and hematin. Pentachlorobenzene and pentachlorophenol were each dechlorinated by vitamin B{sub 12} to yield two out of three possible isomeric tetrachlorobenzenes. Similar relative kinetics and dechlorination products have been observed in anaerobic cultures, suggesting a possible role of transition-metal coenzymes in the reductive dechlorination of poly-chlorinated compounds in natural and engineered environments.

Gantzer, C.J.; Wackett, L.P. (Univ. of Minnesota, Navarre (United States))

1991-04-01

383

The platinum-catalyzed decomposition of methanol: A deceptive demonstration  

SciTech Connect

The platinum-catalyzed gas-phase decomposition of methanol can be used for classroom demonstration in an exciting, interesting fashion. The platinum catalysts, after being heated until it glows, can be made to continue glowing for hours by suspending it over the methanol. This demonstration is useful in a classroom setting for several reasons. First it is more complicated than it appears initially, involving a reaction that is not immediately obvious and is, therefore, more challenging for students to understand. Second, the platinum illustrates the phenomenon of exothermic reactions in a distinctive and memorable way. Because the platinum foil has to be heated before the reactions will proceed, this demonstration also is a perfect example of the temperature dependence of [Delta]G in determining the spontaneity of a reaction. Finally, this demonstration can be used to explain the mutual interaction of two reactions. Because an explanation of this demonstration requires the use of many chemical concepts, it is an ideal activity for stimulating synthesis among students near the end of the course.

Coffing, D.L.; Wile, J.L. (Bell State Univ., Muncie, IN (United States))

1993-07-01

384

Toward antibody-catalyzed hydrolysis of organophosphorus poisons  

PubMed Central

We report here our preliminary results on the use of catalytic antibodies as an approach to neutralizing organophosphorus chemical weapons. A first-generation hapten, methyl-?-hydroxyphosphinate Ha, was designed to mimic the approach of an incoming water molecule for the hydrolysis of exceedingly toxic methylphosphonothioate VX (1a). A moderate protective activity was first observed on polyclonal antibodies raised against Ha. The results were further confirmed by using a mAb PAR 15 raised against phenyl-?-hydroxyphosphinate Hb, which catalyzes the hydrolysis of PhX (1b), a less toxic phenylphosphonothioate analog of VX with a rate constant of 0.36 M?1?min?1 at pH 7.4 and 25°C, which corresponds to a catalytic proficiency of 14,400 M?1 toward the rate constant for the uncatalyzed hydrolysis of 1b. This is a demonstration on the organophosphorus poisons themselves that mAbs can catalytically hydrolyze nerve agents, and a significant step toward the production of therapeutically active abzymes to treat poisoning by warfare agents.

Vayron, Philippe; Renard, Pierre-Yves; Taran, Frederic; Creminon, Christophe; Frobert, Yveline; Grassi, Jacques; Mioskowski, Charles

2000-01-01

385

Heterogeneous catalyzed benzylic acetoxylation of methylated aromatic hydrocarbons  

SciTech Connect

The palladium-catalyzed acetoxylation of toluene to benzyl acetate is highly dependent on particle size. The rate of reaction is highest with 30--35 [Angstrom] particles corresponding to a 0.33 dispersion. Catalysts prepared and reduced by controlled methods before being contacted with the reaction medium, ex situ catalysts, were found to yield lower reaction rates than catalysts prepared in the reaction medium, in situ. Potassium ion-encapsulation in palladium during in situ preparation is a possible explanation for this result. Tin is required to reduce Pd[sup 2+] to Pd[sup 0] in the in situ system, but is not required for the ex situ catalyst. The improvement in activity of the ex situ catalyst in the presence of tin may be due to the reducibility of Sn[sup 4+] to Sn[sup 2+] during oxygen-poor regimes. Results obtained with diverse methylated aromatic hydrocarbons indicate that the aromatic ring interactions with the palladium surface via [pi]-donation before oxidation occurs. 37 refs., 7 figs., 5 tabs.

Benazzi, E.; Mimoun, H.; Cameron, C.J. (Institut Francais du Petrole, Rueil-Malmaison (France))

1993-04-01

386

CuBr-catalyzed oxidative difluoromethylation of tertiary amines with difluoroenol silyl ethers.  

PubMed

CuBr-catalyzed oxidative difluoromethylation of readily available tertiary amines with difluoroenol silyl ethers was performed under mild conditions to afford beta-amine-alpha,alpha-difluoro ketones. PMID:19378964

Chu, Lingling; Zhang, Xingang; Qing, Feng-Ling

2009-05-21

387

Pd-Catalyzed C–H Bond Functionalization on the Indole and Pyrrole Nucleus  

Microsoft Academic Search

\\u000a This review details recent developments in the Pd-catalyzed C–H bond arylation and alkenylation of indoles and pyrroles, aromatic\\u000a heterocycles that are frequently displayed in natural products and medicinal agents.

Elizabeth Beck; Matthew Gaunt

388

Gold-catalyzed hydrative cyclization of 1,6-diynes in ionic liquid media  

Microsoft Academic Search

Gold-catalyzed hydrative cyclization of terminal 1,6-diynes proceeds in ionic liquid with methanol as co-solvent. The solvent-catalyst could be recycled, after separation of the product by extraction with ether.

Dong-Mei Cui; Yi-Na Ke; Dan-Wen Zhuang; Qian Wang; Chen Zhang

2010-01-01

389

Access to the Protoilludane Core by Gold-Catalyzed Allene-vinylcyclopropane Cycloisomerization.  

PubMed

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

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

2013-08-20

390

Exploration of L-Proline-Catalyzed ?-Aminoxylation of Aldehyde to (S)-Guaifenesin-Related Drug Molecules  

Microsoft Academic Search

An efficient enantioselective synthesis of (S)-guaifenesin with >99% ee using L-proline-catalyzed ?-aminoxylation of aldehyde as key step is described and explored for asymmetric syntheses of (S)-moprolol and (R)-methocarbamol.

Sharad P. Panchgalle; Sunita S. Kunte; Subhash P. Chavan; Uttam R. Kalkote

2011-01-01

391

Intramolecular Rhodium-Catalyzed [2 + 2 + 2] Cyclizations of Diynes with Enones  

PubMed Central

The Rh(I)-catalyzed inter- and intramolecular [2 + 2 + 2] cyclization of diynes with ?,?-unsaturated enones proceeds with microwave promotion in good yields. This chemistry was applied to the synthesis of (?)-alcyopterosin I.

Jones, Amanda L.; Snyder, John K.

2009-01-01

392

Catalyzed Ceramic Burner Material. Project Period: August 15, 2010 to March 31, 2012.  

National Technical Information Service (NTIS)

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 th...

A. Barnes R. Charles

2012-01-01

393

Base-catalyzed diastereoselective [3 + 3] annulation of 3-isothiocyanatooxindoles and azomethine imines.  

PubMed

An unprecedented diastereoselective [3 + 3] annulation of 3-isothiocyanatooxindoles and azomethine imines was catalyzed by Et3N, affording 3,3'-triazinyl spirooxindoles in excellent yields and diastereoselectivities under mild conditions. PMID:24047279

Zhu, Gongming; Sun, Wangsheng; Wu, Chongyang; Li, Guofeng; Hong, Liang; Wang, Rui

2013-09-18

394

Stability and evolution of low-surface-tension metal catalyzed growth of silicon nanowires  

NASA Astrophysics Data System (ADS)

Low-surface-tension metals were predicted to be insufficient to catalyze the growth of silicon nanowires (SiNWs) in vapor-liquid-solid (VLS) mode while counter examples do exist, for example, in the tin- or indium-catalyzed SiNWs. This puzzle remains largely unresolved. We first examine the local tension-force-balance in a tin-catalyzed SiNW by using a cross-section analysis. We found that the existence of an ultrathin sidewall-spreading catalyst layer helps to stabilize the catalyst drop during growth. The predicted contact-angle evolution, by an energetic balance model, is also supported by the experimental data. These results bring critical understanding on the low-surface-tension catalyzed VLS process.

Yu, Linwei; Fortuna, Franck; O'Donnell, Benedict; Patriache, Gilles; Roca I Cabarrocas, Pere

2011-03-01

395

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

PubMed Central

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

Schultz, Danielle M.; Wolfe, John P.

2012-01-01

396

Selective reduction of amides to amines by boronic Acid catalyzed hydrosilylation.  

PubMed

Not a 'B'ore! Benzothiophene-based boronic acids catalyze the reduction of tertiary, secondary, and primary amides in the presence of a hydrosilane. The reaction demonstrates good functional-group tolerance. PMID:24014044

Li, Yuehui; Molina de La Torre, Jesús A; Grabow, Kathleen; Bentrup, Ursula; Junge, Kathrin; Zhou, Shaolin; Brückner, Angelika; Beller, Matthias

2013-09-06

397

Rhodium-catalyzed decarbonylative C-H arylation of 2-aryloxybenzoic acids leading to dibenzofuran derivatives.  

PubMed

Rhodium-catalyzed intramolecular C-H arylation of 2-aryloxybenzoic acids proceeded accompanied by decarbonylation to give dibenzofuran derivatives in high yields. The present reaction is widely applicable to substrates bearing various functionalities. PMID:23679209

Maetani, Shinji; Fukuyama, Takahide; Ryu, Ilhyong

2013-05-16

398

Regioselective Reduction of Polynuclear Heteroaromatics Catalyzed by Transition Metal Complexes and Hydrodenitrogenation Chemistry.  

National Technical Information Service (NTIS)

The use of transition metal complexes as catalysts for the reduction of the heteroatom containing ring in polynuclear heteroaromatic compounds has been investigated. Additionally, a study has been made of the heterogeneously catalyzed cleavage of carbon-n...

A. D. Thormodsen T. Vermeulen R. H. Fish

1985-01-01

399

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...

400

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

EPA Science Inventory

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

401

Copper-catalyzed oxidation of arene-fused cyclic amines to cyclic imides.  

PubMed

A novel copper-catalyzed oxidation of arene-fused cyclic amines to the corresponding cyclic imides has been developed. The reaction can be used to synthesize 1,3-disubstituted TPD in high yields. PMID:24100546

Yan, Xiaoyu; Fang, Kun; Liu, Hailan; Xi, Chanjuan

2013-10-17

402

Rhodium catalyzed enantioselective cyclization of substituted imidazoles via C-H bond activation.  

PubMed

The enantioselective intramolecular alkylation of substituted imidazoles with enantiomeric excesses up to 98% has been accomplished by rhodium catalyzed C-H bond functionalization with (S,S',R,R')TangPhos as the chiral ligand. PMID:19662249

Tsai, Andy S; Wilson, Rebecca M; Harada, Hitoshi; Bergman, Robert G; Ellman, Jonathan A

2009-06-02

403

Access to the Protoilludane Core by Gold-Catalyzed Allene-vinylcyclopropane Cycloisomerization  

PubMed Central

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

2013-01-01

404

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...

405

Environmental assessment of the base catalyzed decomposition (BCD) process. Research report, June--July 1998  

SciTech Connect

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

NONE

1998-08-01

406

Enzyme Catalyzed 2-D Polymerization of Phenol and Aniline Derivatives on a Langmuir-Blodgett Through.  

National Technical Information Service (NTIS)

Previous studies have shown that polymeric materials may be synthesized from substituted phenols and aromatic amine compounds through a Horseradish Peroxidase (HRP) enzyme catalyzed reaction in the bulk. We have developed a novel approach for this enzyme ...

F. Bruno J. A. Akkara L. A. Samuelson B. K. Mandal D. L. Kaplan

1992-01-01

407

On the Role of CO2 in NHC-Catalyzed Oxidation of Aldehydes  

PubMed Central

NHC-catalyzed oxidations using carbon dioxide as the stoichiometric oxidant have been carefully investigated. These studies support a secondary role of CO2 in suppressing side reactions and exogenous oxygen as the actual oxidant.

Chiang, Pei-Chen; Bode, Jeffrey W.

2011-01-01

408

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

National Technical Information Service (NTIS)

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

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

1998-01-01

409

Chloride effect on the palladium-catalyzed allylic substitution vs elimination of cyclic vinyloxazolidinones and oxazolines  

Microsoft Academic Search

The introduction of catalytic amounts of lithium chloride, or the utilization of chloride containing catalyst sources completely inhibited elimination in the Pd-catalyzed allylic substitution of vinyloxazolidinones and oxazolines.

Gregory R. Cook; P. Sathya Shanker

1998-01-01

410

Convergence of mechanistic pathways in the Palladium(0)-catalyzed cross-coupling of alkenylsilacyclobutanes and alkenylsilanols  

PubMed

Alkenylsilacyclobutanes and alkenylsilanols react in palladium-catalyzed cross-coupling reactions via the same intermediate, produced in situ upon treatment of either starting material with tetrabutylammonium fluoride. PMID:10956529

Denmark; Wehrli; Choi

2000-08-10

411

Rh-catalyzed reductive coupling reaction of aldehydes with conjugated dienes promoted by triethylborane.  

PubMed

Rh(I) catalyzes the reductive coupling reaction of a wide variety of aldehydes with conjugated dienes in the presence of a stoichiometric amount of triethylborane to provide homoallyl alcohols in a single operation. PMID:19663391

Kimura, Masanari; Nojiri, Daisuke; Fukushima, Masahiro; Oi, Shuichi; Sonoda, Yusuke; Inoue, Yoshio

2009-09-01

412

Hf(IV)-Catalyzed Enantioselective Epoxidation of N-Alkenyl Sulfonamides and N-Tosyl Imines  

PubMed Central

Asymmetric epoxidation of allylic and homoallylic amine derivatives catalyzed by Hf(IV)-bishydroxamic acid complexes is described. Under similar conditions, aldimine and ketimine produced oxaziridines. The sulfonyl group is demonstrated to be an effective directing group for these transformations.

Olivares-Romero, Jose Luis; Li, Zhi; Yamamoto, Hisashi

2012-01-01

413

Nickel-catalyzed borylation of halides and pseudohalides with tetrahydroxydiboron [B2(OH)4].  

PubMed

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 pseudohalides 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

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

2013-06-18

414

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

PubMed

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

Sydor, Paulina K; Challis, Gregory L

2012-01-01

415

Pd(II)-Catalyzed ortho-Alkylation of Benzoic Acids with Alkyl Halides  

PubMed Central

The first Pd(II)-catalyzed alkylation of aryl C–H bonds is achieved without using a co-oxidant. The alkylation reaction was followed thereafter by an intramolecular lactonization to give broadly useful ?– and ™– benzolactones.

Zhang, Yang-Hui; Shi, Bing-Feng; Yu, Jin-Quan

2010-01-01

416

Synthesis of Fused-?-Lactams through Selective Gold-Catalyzed Oxycyclization of Dioxolane-Tethered Enynes.  

PubMed

The gold-catalyzed preparation of 2-azetidinone-fused oxacycles was accomplished from ?-lactam-linked enynes through heterocyclization reaction taking advantage of the acetonide pendant group. While the synthesis of fused tetrahydrofuran-?-lactams from 1,3-enynes could be considered as an unusual metal-catalyzed cyclization of enynols, ?-alkoxy dioxolane-tethered 1,3-enynes exclusively undergo bis-oxycyclization to afford tricyclic bridged acetals. PMID:24007239

Alcaide, Benito; Almendros, Pedro; Martínez Del Campo, Teresa; Torres, M Rosario

2013-09-11

417

Oxidative 4-dechlorination of polychlorinated phenols is catalyzed by extracellular fungal lignin peroxidases  

Microsoft Academic Search

The extracellular lignin peroxidases (ligninases) of Phanerochaete chrysosporium catalyzed HâOâ-dependent spectral changes in several environmentally significant polychlorinated phenols: 2,4-dichloro-, 2,4,5-trichloro-, 2,4,6-trichloro-, and pentachlorophenol. Gas chromatography\\/mass spectrometry of reduced and acetylated reaction products showed that, in each case, lignin peroxidase catalyzed a 4-dechlorination of the starting phenol to yield a p-benzoquinone. The oxidation of 2,4-dichlorophenol also yielded a dechlorinated coupling dimer,

Kenneth E. Hammel; Paul J. Tardone

1988-01-01

418

New palladium-catalyzed reactions of unsaturated triflates with alkenes and alkyenes  

Microsoft Academic Search

The palladium-catalyzed reaction of vinyl triflates with P-substituted-a,P- unsaturated carbonyl compounds affords regio- and stereoselectively the corresponding vinylic substitution derivatives. The application of this reaction to the synthesis of quinolines, coumarins, and cardenolides is described. The palladium- catalyzed reaction of unsaturated triflates with functionalized internal and terminal alkynes produces a variety of heterocyclic compounds such as furans, benzo(hIfurans, indoles, butenolides,

Sandro Cacchi

1996-01-01

419

Immunoglobulins can utilize riboflavin (Vitamin B2) to activate the antibody-catalyzed water oxidation pathway  

Microsoft Academic Search

We have recently discovered a reaction that all antibodies, regardless of source or antigenic specificity can catalyze, that is the reaction between singlet dioxygen (1O2*) and H2O to generate H2O2. We have named this process the antibody-catalyzed water oxidation pathway (ACWOP). As part of our ongoing investigations into the possible biological role of this pathway, we have studied whether isoalloxazine-containing

Jorge Nieva; Lisa Kerwin; Anita D. Wentworth; Richard A. Lerner; Paul Wentworth

2006-01-01

420

Transition-metal-catalyzed synthesis of aspergillide B: an alkyne addition strategy.  

PubMed

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

Trost, Barry M; Bartlett, Mark J

2012-02-22

421

Enzyme-catalyzed processes of first-pass hepatic and intestinal drug extraction  

Microsoft Academic Search

Oral bioavailability of pharmacologically effective drugs is often limited by first-pass biotransformation. In humans, both hepatic and intestinal enzymes can catalyze the metabolism of a drug as it transits between the gastrointestinal lumen and systemic blood for the first time. Although a spectrum of drug biotransformations can occur during first-pass, the most common are oxidations catalyzed by cytochromes P450. It

Kenneth E. Thummel; Kent L. Kunze; Danny D. Shen

1997-01-01

422

Effects of Sulfhydryl Compounds on Lipid Oxidations Catalyzed by Copper and Heme  

Microsoft Academic Search

A B ST R A CT Effects of cysteine and glutathione on copper- and heme-catalyzed oxidation of methyl linoleate were studied in a model emulsion system. In the copper-catalyzed system, cysteine exerted a strong prooxi- dative effect, and this prooxi~lative effect increased as the concentration of cysteine increased. Furthermore, oxidized gluta- thione did not have a prooxidative ef)~ect, whereas reduced

J. J. Yee; W. F. Shipe

1982-01-01

423

An electrochemical nickel-catalyzed arylation of 3-amino-6-chloropyridazines.  

PubMed

3-Amino-6-aryl- and 3-amino-6-heteroarylpyridazines have been obtained in generally good yield using a nickel-catalyzed electrochemical cross-coupling between 3-amino-6-chloropyridazines and aryl or heteroaryl halides at room temperature. Comparative experiments involving classical palladium-catalyzed reactions, such as Suzuki, Stille, or Negishi cross-couplings, reveal that the electrochemical method can constitute a reliable alternative tool for biaryl formation. A possible reaction mechanism is proposed on the basis of electrochemical analyses. PMID:23241172

Sengmany, Stéphane; Vitu-Thiebaud, Arnaud; Le Gall, Erwan; Condon, Sylvie; Léonel, Eric; Thobie-Gautier, Christine; Pipelier, Muriel; Lebreton, Jacques; Dubreuil, Didier

2013-01-04

424

Intensity Oscillation of Chemiluminescence in Ferroin-Catalyzed Belousov-Zhabotinsky Reaction  

Microsoft Academic Search

A weak chemiluminescence phenomenon was observed in ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction. The luminescence intensity oscillated with the self- oscillation of the visible color change and redox potential change in anti phase. A periodic signal of the luminescence was also detected even after the extinction of the self- oscillation. These results showed that the ferroin-catalyzed system has additional oscillatory reaction which

Osamu INOMOTO; Tomoyuki OHYA; Shoichi KAI

2000-01-01

425

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

PubMed

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

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

2012-04-25

426

Iron-catalyzed cross-coupling reactions of alkyl Grignards with aryl sulfamates and tosylates.  

PubMed

The iron-catalyzed cross-coupling of aryl sulfamates and tosylates has been achieved with primary and secondary alkyl Grignards. This study of iron-catalyzed cross-coupling reactions also examines the isomerization and ?-hydride elimination problems that are associated with the use of isopropyl nucleophiles. While a variety of iron sources were competent in the reaction, the use of FeF(3)•3H(2)O was critical to minimize nucleophile isomerization. PMID:23244161

Agrawal, Toolika; Cook, Silas P

2012-12-17

427

Nickel-Catalyzed Amination of Aryl Sulfamates and Carbamates Using an Air-Stable Precatalyst  

PubMed Central

A facile nickel-catalyzed method to achieve the amination of synthetically useful aryl sulfamates and carbamates is reported. Contrary to most Ni-catalyzed amination reactions, this user-friendly approach relies on an air-stable Ni(II) precatalyst, which, when employed with a mild reducing agent, efficiently delivers aminated products in good to excellent yields. The scope of the method is broad with respect to both coupling partners and includes heterocyclic substrates.

Hie, Liana; Ramgren, Stephen D.; Mesganaw, Tehetena; Garg, Neil K.

2012-01-01

428

Nickel-catalyzed amination of aryl sulfamates and carbamates using an air-stable precatalyst.  

PubMed

A facile nickel-catalyzed method to achieve the amination of synthetically useful aryl sulfamates and carbamates is reported. Contrary to most Ni-catalyzed amination reactions, this user-friendly approach relies on an air-stable Ni(II) precatalyst, which, when employed with a mild reducing agent, efficiently delivers aminated products in good to excellent yields. The scope of the method is broad with respect to both coupling partners and includes heterocyclic substrates. PMID:22849697

Hie, Liana; Ramgren, Stephen D; Mesganaw, Tehetena; Garg, Neil K

2012-07-31

429

Diverse reactions catalyzed by naphthalene dioxygenase from Pseudomonas sp strain NCIB 9816  

Microsoft Academic Search

Naphthalene dioxygenase (NDO) fromPseudomonas sp strain NCIB 9816 is a multicomponent enzyme system which initiates naphthalene catabolism by catalyzing the addition of both atoms of molecular oxygen and two hydrogen atoms to the substrate to yield enantiomerically pure (+)-cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene. NDO has a relaxed substrate specificity and catalyzes the dioxygenation of many related 2- and 3-ring aromatic and hydroaromatic (benzocyclic) compounds

SM Resnick; K Lee; DT Gibson

1996-01-01

430

A highly efficient buckypaper-based electrode material for mediatorless laccase-catalyzed dioxygen reduction  

Microsoft Academic Search

The redox enzyme laccase from Trametes versicolor efficiently catalyzes the oxygen reduction reaction (ORR) in mediatorless biofuel cell cathodes when adsorbed onto multi-walled carbon nanotubes (MWCNTs). In this work we demonstrate that the fabrication of MWCNTs in form of buckypaper (BP) results in an excellent electrode material for laccase-catalyzed cathodes.BPs are mechanically stable, self-entangling mats with high dispersion of MWCNTs

L. Hussein; S. Rubenwolf; F. von Stetten; G. Urban; R. Zengerle; M. Krueger; S. Kerzenmacher

2011-01-01

431

Oxidation of 8-hydroxyquinoline catalyzed by laccase from Trametes pubescens yields an antioxidant aromatic polymer  

Microsoft Academic Search

We report for the first time the enzyme-catalyzed production of poly (8-hydroxyquinoline) using laccase from the white rot fungus Trametes pubescens (CBS 696.94). The oxidative polymerisation of 8-hydroxyquinoline was catalyzed by laccase in a reaction medium containing 8% acetone, 0.01–0.05mg\\/ml 8-hydroxyquinoline and sodium acetate buffer (0.1M, pH 5.0) at 30°C. The average molecular weight of the polymeric product, as determined

Sandile Ncanana; Stephanie Burton

2007-01-01

432

Palladium-Catalyzed Chemoselective Decarboxylative Ortho Acylation of Benzoic Acids with ?-Oxocarboxylic Acids.  

PubMed

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

Miao, Jinmin; Ge, Haibo

2013-05-30

433

Germanium-catalyzed hierarchical Al(2)O(3) and SiO(2) nanowire bunch arrays.  

PubMed

Germanium (Ge), a Group IV semiconductor, was recently used as an effective catalyst to grow individual, single-crystalline ZnO nanowires through a vapor-liquid-solid (VLS) process [Pan et al., Angew. Chem., Int. Ed., 2005, 44, 274-278]. Here, we show that Ge can also act as an efficient catalyst for the large-scale growth of highly aligned, closely-packed polycrystalline Al(2)O(3) and amorphous SiO(2) nanowire bunch arrays. The Ge-catalyzed Al(2)O(3) and SiO(2) nanowire growth exhibits many interesting growth behaviors including (i) multiple nanowire growth catalyzed by one micrometer-size Ge particle, (ii) branching growth and (iii) batch-by-batch growth. These growth phenomena are distinct from the conventional Au-catalyzed nanowire growth but are analogous to the recently reported Ga-catalyzed SiO(2) nanowire growth. It is anticipated that many other oxide nanowires and nanowire assemblies can be synthesized through the Ge-catalyzed VLS process. The Ge-catalyzed Al(2)O(3) and SiO(2) nanowires emit strong visible light under ultraviolet light excitation. PMID:20648272

Gu, Zhanjun; Liu, Feng; Howe, Jane Y; Parans Paranthaman, M; Pan, Zhengwei

2009-09-23

434

Kinetics of catalyzed sodium borohydride hydrolysis and fuel cell applicability  

NASA Astrophysics Data System (ADS)

Metal boride catalysts have been developed through reduction of (Ni, Co, and Ru) metal salts with sodium borohydride solutions. The resulting metal borides were determined to be Ni3B, Co3B, and elemental Ru by use of XRD analysis. SEM images give the particle size of the catalyst to be in the range or 65-150nm. Optimum heat treatment for the samples was determined to be 150°C for Ni3B, 200°C for Co3B, and 400°C for Ru. Ruthenium catalysts were found to have the greatest catalytic activity followed by cobalt boride and nickel boride. Hydrolysis testing with nickel boride catalysts has shown that the maximum hydrolysis rate as a function of sodium borohydride occurs at 5-10 wt% NaBH 4 when considered in solution with 5 wt% NaOH. The hydrolysis rate increases for the nickel boride catalyst with increasing NaOH concentration. Tests were performed at elevated pressures and showed that reaction rate could be controlled and even stopped with sufficient hydrogen pressures on the order of 10 MPa. Decreases in system pressure cause the reaction rate to increase, which tends to maintain the system at the equilibrium pressure. Thus, a high pressure hydrogen generator is considered. 210mg of Co3B catalyst in a 30 wt% solution of sodium borohydride can produce 30kW of hydrogen electrical power equivalent if utilized within a fuel cell operating at 40% efficiency. A semi-empirical isotherm model has been developed to accurately calculate the reaction rate for a Co3B catalyzed reaction as a function of temperature (35-80°C) and pressure (0.1-10MPa).

Walter, Joshua C.

435

A thermodynamic investigation of reactions catalyzed by tryptophan synthase.  

PubMed

Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of the following reactions catalyzed by the tryptophan synthase alpha 2 beta 2 complex (EC 4.2.1.20) and its subunits: indole(aq) + L-serine(aq) = L-tryptophan(aq) + H2O(1); L-serine(aq) = pyruvate(aq) + ammonia(aq); indole(aq) + D-glyceraldehyde 3-phosphate(aq) = 1-(indol-3-yl)glycerol 3-phosphate(aq); L-serine(aq) + 1-(indol-3-yl)glycerol 3-phosphate(aq) = L-tryptophan(aq) + D-glyceraldehyde 3-phosphate(aq) + H2O(1). The calorimetric measurements led to standard molar enthalpy changes for all four of these reactions. Direct measurements yielded an apparent equilibrium constant for the third reaction; equilibrium constants for the remaining three reactions were obtained by using thermochemical cycle calculations. The results of the calorimetric and equilibrium measurements were analyzed in terms of a chemical equilibrium model that accounted for the multiplicity of the ionic states of the reactants and products. Thermodynamic quantities for chemical reference reactions involving specific ionic forms have been obtained. These quantities permit the calculation of the position of equilibrium of the above four reactions as a function of temperature, pH, and ionic strength. Values of the apparent equilibrium constants and standard transformed Gibbs free energy changes delta r G'(m) degree under approximately physiological conditions are given. Le Châtelier's principle provides an explanation as to why, in the metabolic pathway leading to the synthesis of L-tryptophan, the third reaction proceeds in the direction of formation of indole and D-glyceraldehyde 3-phosphate even though the apparent equilibrium constant greatly favors the formation of 1-(indol-3-yl)glycerol 3-phosphate. PMID:9700925

Kishore, N; Tewari, Y B; Akers, D L; Goldberg, R N; Miles, E W

1998-07-27

436

Kinetic modeling of interesterification reactions catalyzed by immobilized lipase.  

PubMed

Kinetic data for lipase-catalyzed interesterification reactions between free fatty acids and triglycerides were collected and the dynamics of the interesterification reactions were successfully modeled using tow rate experssions requiring a total of five adjustable parameters. One rate expression describes the disappearance of the free fatty acid (octanoic or linolenic acid), and the second describes the rate of release of fatty acid residues from the triglycerides (olive oil or milkfat). This model is able to account for the effects of the concentration of all chemical species participating in interesterification throughout the entire reaction. When the data for both milkfat and olive oil were subjected to nonlinear regression analyses using the same mathematical model, the parameter estimates for both systems were comparable. In addition to reproducing the tendencies observed experimentally, simulations of the interesterification system under a variety of initial conditions provided insight into the effects of several reaction variables which could not be examined experimentally. Among the most significant findings of the simulation work are (1) there is a limit beyond which increasing the initial concentration of water produces no further increase in the initial rate of the interesterification reaction; (2) an increase in the initial concentration of lower glycerides produces a concomitant increase in the rate of the interesterification reaction; (3) the free fatty acids inhibit the rate of hydrolysis of the fatty acid residues of the triglycerides; (4) there is a limit beyond which increasing the initial concentration of triglycerides produces no significant increase in the rate of either the hydrolysis reaction or the interesterification reaction. PMID:18615612

Reyes, H R; Hill, C G

1994-01-20

437

The mechanism for iron-catalyzed alkene isomerization in solution  

SciTech Connect

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

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

2008-05-27

438

Quantitative studies of caspase-3 catalyzed ?II-spectrin breakdown.  

PubMed

Under various physiological and patho-physiological conditions, spectrin breakdown reactions generate several spectrin breakdown products (SBDPs)-in particular SBDPs of 150kDa (SBDP150) and 120kDa (SBDP120). Recently, numerous studies have shown that reactions leading to SBDPs are physiologically relevant, well regulated, and complex. Yet molecular studies on the mechanism of the SBDP formation are comparatively scarce. We have designed basic systems to allow us to follow the breakdown of ?II-spectrin model proteins by caspase-3 in detail with gel electrophoresis, fluorescence and mass spectrometry methods. Amongst the predicted and reported sites, our results show that caspase-3 cleaves after residues D1185 and D1478, but not after residues D888, D1340 and D1475. We also found that the cleavage at these two sites is independent of each other. It may be possible to inhibit one site without affecting the other site. Cleavage after residue D1185 in intact ?II-spectrin leads to SBDP150, and cleavage after D1478 site leads to SBDP120. Our results also show that the cleavage after the D1185 residue is unusually efficient, with a kcat/KM value of 40,000M(-1)s(-1), and the cleavage after the D1478 site is more similar to most of the other reported caspase-3 substrates, with a kcat/KM value of 3000M(-1)s(-1). We believe that this study lays out a methodology and foundation to study caspase-3 catalyzed spectrin breakdown to provide quantitative information. Molecular understanding may lead to better understanding of brain injuries and more precise and specific biomarker development. PMID:23948103

Witek, Marta A; Fung, L W-M

2013-08-12

439

Investigating antibody-catalyzed ozone generation by human neutrophils  

PubMed Central

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

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

2003-01-01

440

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

PubMed Central

The growth of semiconductor (SC) nanowires (NW) by CVD using Au-catalyzed VLS process has been widely studied over the past few years. Among others SC, it is possible to grow pure Si or SiGe NW thanks to these techniques. Nevertheless, Au could deteriorate the electric properties of SC and the use of other metal catalysts will be mandatory if NW are to be designed for innovating electronic. First, this article's focus will be on SiGe NW's growth using Au catalyst. The authors managed to grow SiGe NW between 350 and 400°C. Ge concentration (x) in Si1-xGex NW has been successfully varied by modifying the gas flow ratio: R = GeH4/(SiH4 + GeH4). Characterization (by Raman spectroscopy and XRD) revealed concentrations varying from 0.2 to 0.46 on NW grown at 375°C, with R varying from 0.05 to 0.15. Second, the results of Si NW growths by CVD using alternatives catalysts such as platinum-, palladium- and nickel-silicides are presented. This study, carried out on a LPCVD furnace, aimed at defining Si NW growth conditions when using such catalysts. Since the growth temperatures investigated are lower than the eutectic temperatures of these Si-metal alloys, VSS growth is expected and observed. Different temperatures and HCl flow rates have been tested with the aim of minimizing 2D growth which induces an important tapering of the NW. Finally, mechanical characterization of single NW has been carried out using an AFM method developed at the LTM. It consists in measuring the deflection of an AFM tip while performing approach-retract curves at various positions along the length of a cantilevered NW. This approach allows the measurement of as-grown single NW's Young modulus and spring constant, and alleviates uncertainties inherent in single point measurement.

2011-01-01

441

Development of a second generation palladium-catalyzed cycloalkenylation and its application to bioactive natural product synthesis.  

PubMed

A novel palladium-catalyzed intramolecular oxidative alkylation of unactivated olefins is described. This protocol was devised to solve one of the drawbacks of the original palladium-catalyzed cycloalkenylation that we developed. We call this new procedure the 'second generation palladium-catalyzed cycloalkenylation'. This protocol has been applied to the total syntheses of cis-195A, trans-195A, boonein, scholareins A, C, D, and alpha-skytanthine. PMID:23980435

Toyota, Masahiro

2013-07-01

442

Development of Pd–Cu catalyzed cross-coupling of terminal acetylenes with sp 2-carbon halides  

Microsoft Academic Search

The Pd-catalyzed cross coupling reactions between sp2-C halides and terminal acetylenes have been independently reported by Heck, Cassar and us in 1975. The former two methods have been developed as an extension of the Heck reaction to an acetylenic CH-bond. Ours has been discovered on the base of combination of Pd-catalyzed cross-coupling of sp2-C halides with terminal acetylenes and Cu-catalyzed

Kenkichi Sonogashira

2002-01-01

443

Asymmetric oxidation of sulfides catalyzed by titanium and vanadium complexes in the synthesis of biologically active sulfoxides  

NASA Astrophysics Data System (ADS)

Published data on the asymmetric synthesis of chiral biologically active sulfoxides by oxidation of appropriate sulfides catalyzed by titanium and vanadium complexes are generalized. Bibliography — 87 references.

Volcho, Konstantin P.; Salakhutdinov, Nariman F.

2009-05-01

444

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

Microsoft Academic Search

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

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

2002-01-01

445

A single amino acid residue determines the ratio of hydrolysis to transglycosylation catalyzed by ?-glucosidases.  

PubMed

The propensity to catalysis of transglycosylation of the ?-glucosidase Tm?gly is higher than for Sf?gly. Moreover the propensity to catalysis of transglycosylation is directly proportional to the substrate concentration for Tm?gly, whereas for Sf?gly it is constant. For instance, 60% of a Tm?gly sample catalyzes transglycosylation reactions at 40 mM p-nitrophenyl ?-glucoside, whereas only 40% is engaged in hydrolysis of this substrate. For Sf?gly the fraction involved in transglycosylation is only 30 %. In addition, 48 % of a Tm?gly sample catalyzes transglycosylation reactions at 8 mM methylumbelliferyl ?-glucoside, whereas Sf?gly does not catalyze transglycosylation using this substrate. Interestingly, these Tm?gly properties were grafted into Sf?gly by a single replacement of a residue forming a channel involved in supplying the catalytic water molecules for attack on the covalent intermediate present in the reaction catalyzed by ?-glucosidases. Hence a single residue determines the ratio of hydrolysis to transglycosylation reactions catalyzed by these ?-glucosidases. PMID:22670763

Frutuoso, M A; Marana, S R

2013-01-01

446

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

PubMed Central

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

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

2008-01-01

447

Removal of SU-8 resists using hydrogen radicals generated by tungsten hot-wire catalyzer  

NASA Astrophysics Data System (ADS)

We investigated removal of chemically amplified negative-tone i-line resist SU-8 using hydrogen radicals, which was generated by the catalytic decomposition of H2/N2 mixed gas (H2:N2 = 10:90vol.%) using tungsten hot-wire catalyzer. SU-8 with exposure dose from 7 (Dg100×0.5) to 280mJ/cm2 (Dg100×20) were removed by hydrogen radicals without a residual layer. When the distance between the catalyzer and the substrate was 100mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was 50°C, removal rate of SU-8 was 0.17?m/min independent of exposure dose to the SU-8. Finally, we obtained high removal rate for SU-8 (exposure dose = 14mJ/cm2 (Dg100)) of approximately 4?m/min when the distance between the catalyzer and the substrate was 20mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was 165°C.

Kono, Akihiko; Arai, Yu; Goto, Yousuke; Horibe, Hideo

2012-03-01

448

Carbocyclization versus oxycyclization on the metal-catalyzed reactions of oxyallenyl C3-linked indoles.  

PubMed

The preparation of previously unknown (indol-3-yl)-?-allenols and -allenones was accomplished from indole-3-carbaldehydes, through indium-mediated Barbier allenylation reaction taking advantage of the N-(2-pyridyl)sulfonyl group. Metal-catalyzed cyclizations of oxyallenyl C3-linked indoles proceeded in two ways depending on the presence or absence of the N-(2-pyridyl)sulfonyl group. For allenols, gold-catalyzed oxycyclization occurred in the presence of the protecting group; in the absence of the protecting group, palladium- and gold-catalyzed benzannulations operated. On the contrary, under gold catalysis furyl-indoles were obtained as exclusive products from NH-allenones, while 5-endo carbocyclization adducts were the major components starting from N-SO2py-protected allenones. These cyclization reactions have been developed experimentally, and their mechanisms have additionally been investigated by a computational study. PMID:23738835

Alcaide, Benito; Almendros, Pedro; Alonso, José M; Fernández, Israel

2013-06-18

449

Iridium-catalyzed allylic vinylation and asymmetric allylic amination reactions with o-aminostyrenes.  

PubMed

An Ir-catalyzed allylic vinylation reaction of allyl carbonates with o-aminostyrene derivatives has been realized, providing skipped (Z,E)-diene derivatives. With (E)-but-2-ene-1,4-diyl dimethyl dicarbonate as the substrate, an efficient enantioselective synthesis of 1-benzazepine derivatives via an Ir-catalyzed domino allylic vinylation/intramolecular allylic amination reaction has been developed. Mechanistic studies of the allylic vinylation reaction have been carried out, and the results suggest that the leaving group of the allylic precursor plays a key role in directing the reaction pathway. Screening of various allylic precursors showed that Ir-catalyzed reactions of allyl diethyl phosphates with o-aminostyrene derivatives proceed via an allylic amination pathway. A subsequent ring-closing metathesis (RCM) reaction of the amination products led to a series of enantiomerically enriched 1,2-dihydroquinoline derivatives. Their utility is indicated by an asymmetric total synthesis of (-)-angustureine. PMID:21995503

Ye, Ke-Yin; He, Hu; Liu, Wen-Bo; Dai, Li-Xin; Helmchen, Günter; You, Shu-Li

2011-11-02

450

Phosphoramidite Gold(I)-Catalyzed Diastereo- and Enantioselective Synthesis of 3,4-Substituted Pyrrolidines  

PubMed Central

In this article the utility of phosphoramidite ligands in enantioselective AuI catalysis was explored in the development of highly diastereo- and enantioselective AuI-catalyzed cycloadditions of allenenes. A AuI-catalyzed synthesis of 3,4-disubstituted pyrrolidines and ?-lactams is described. This reaction proceeds through the enantioselective AuI-catalyzed cyclization of allenenes to form a carbocationic intermediate that is trapped by an exogenous nucleophile, resulting in the highly diastereoselective construction of three contiguous stereogenic centers. A computational study (DFT) was also performed to gain some insight into the underlying mechanisms of these cycloadditions. The utility of this new methodology was demonstrated through the formal synthesis of (–)-isocynometrine.

Gonzalez, Ana Z.; Benitez, Diego; Tkatchouk, Ekaterina; Goddard, William A.; Toste, F. Dean

2011-01-01

451

Olefin cyclopropanation via carbene transfer catalyzed by engineered cytochrome P450 enzymes.  

PubMed

Transition metal-catalyzed transfers of carbenes, nitrenes, and oxenes are powerful methods for functionalizing C=C and C-H bonds. Nature has evolved a diverse toolbox for oxene transfers, as exemplified by the myriad monooxygenation reactions catalyzed by cytochrome P450 enzymes. The isoelectronic carbene transfer to olefins, a widely used C-C bond-forming reaction in organic synthesis, has no biological counterpart. Here we report engineered variants of cytochrome P450(BM3) that catalyze highly diastereo- and enantioselective cyclopropanation of styrenes from diazoester reagents via putative carbene transfer. This work highlights the capacity to adapt existing enzymes for the catalysis of synthetically important reactions not previously observed in nature. PMID:23258409

Coelho, Pedro S; Brustad, Eric M; Kannan, Arvind; Arnold, Frances H

2012-12-20

452

Primary product of the horseradish peroxidase-catalyzed oxidation of pentachlorophenol  

SciTech Connect

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

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

1999-05-01

453

Enhancement of enzymatic digestibility of Eucalyptus grandis pretreated by NaOH catalyzed steam explosion.  

PubMed

NaOH catalyzed steam explosion was applied to improve the enzymatic digestibility of Eucalyptus grandis. The impregnation of wood chip with NaOH solutions before steam explosion was carried out to investigate the effects of alkaline catalysis on solid recovery, enzymatic digestibility, and glucose recovery. The lignin removal was significantly affected by NaOH as a catalyst and the glucose recovery increased with increased severity index. The use of NaOH showed higher enzymatic digestibility than the use of water at most severity indexes due to the delignification of biomass and the increase of accessibility to cellulose of enzyme. The maximum glucose recovery was 65.55% having 4.4361 of severity index with 7wt.% of NaOH catalyzed steam explosion at 210°C during 9min. NaOH catalyzed steam explosion was effective to enhance the enzymatic digestibility due to the removal of lignin. PMID:22939603

Park, Ji-Yeon; Kang, Minsu; Kim, Jun Seok; Lee, Joon-Pyo; Choi, Won-Il; Lee, Jin-Suk

2012-07-31

454

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

PubMed

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

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

2012-01-15

455

Bulk Gold-Catalyzed Reactions of Isocyanides, Amines, and Amine N-Oxides  

SciTech Connect

Bulk gold powder (5–50 ?m particles) catalyzes the reactions of isocyanides with amines and amine N-oxides to produce ureas. The reaction of n-butyl isocyanide (nBu–N?C) with di-n-propylamine and N-methylmorpholine N-oxide in acetonitrile, which was studied in the greatest detail, produced 3-butyl-1,1-dipropylurea (O?C(NHnBu)(NnPr2)) in 99% yield at 60 °C within 2 h. Sterically and electronically different isocyanides, amines, and amine N-oxides react successfully under these conditions. Detailed studies support a two-step mechanism that involves a gold-catalyzed reaction of adsorbed isocyanide with the amine N-oxide to form an isocyanate (RN?C?O), which rapidly reacts with the amine to give the urea product. These investigations show that bulk gold, despite its reputation for poor catalytic activity, is capable of catalyzing these reactions.

Klobukowski, Erik; Angelici, Robert; Woo, Keith L.

2012-01-26

456

RNA as an RNA Polymerase: Net Elongation of an RNA Primer Catalyzed by the Tetrahymena Ribozyme  

NASA Astrophysics Data System (ADS)

A catalytic RNA (ribozyme) derived from an intervening sequence (IVS) RNA of Tetrahymena thermophila will catalyze an RNA polymerization reaction in which pentacytidylic acid (C5) is extended by the successive addition of mononucleotides derived from a guanylyl-(3', 5')-nucleotide (GpN). Cytidines or uridines are added to C5 to generate chain lengths of 10 to 11 nucleotides, with longer products being generated at greatly reduced efficiency. The reaction is analogous to that catalyzed by a replicase with C5 acting as the primer, GpNs as the nucleoside triphosphates, and a sequence in the ribozyme providing a template. The demonstration that an RNA enzyme can catalyze net elongation of an RNA primer supports theories of prebiotic RNA self-replication.

Been, Michael D.; Cech, Thomas R.

1988-03-01

457

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

PubMed

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

Xu, Wen-Ying; Gao, Ting-Yao

2007-01-01

458

Assessing the regioselectivity of OleD-catalyzed glycosylation with a diverse set of acceptors.  

PubMed

To explore the acceptor regioselectivity of OleD-catalyzed glucosylation, the products of OleD-catalyzed reactions with six structurally diverse acceptors flavones- (daidzein), isoflavones (flavopiridol), stilbenes (resveratrol), indole alkaloids (10-hydroxycamptothecin), and steroids (2-methoxyestradiol)-were determined. This study highlights the first synthesis of flavopiridol and 2-methoxyestradiol glucosides and confirms the ability of OleD to glucosylate both aromatic and aliphatic nucleophiles. In all cases, molecular dynamics simulations were consistent with the determined product distribution and suggest the potential to develop a virtual screening model to identify additional OleD substrates. PMID:23360118

Zhou, Maoquan; Hamza, Adel; Zhan, Chang-Guo; Thorson, Jon S

2013-01-29

459

Gold(I)-Catalyzed Intramolecular Amination of Allylic Alcohols With Alkylamines  

PubMed Central

A 1:1 mixture of (1)AuCl [1 = P(t-Bu)2o-biphenyl] and AgSbF6 catalyzes the intramolecular amination of allylic alcohols with alkylamines to form substituted pyrrolidine and piperidine derivatives. Gold(I)-catalyzed cyclization of (R,Z)-8-(N-benzylamino)-3-octen-2-ol (96% ee, 95% de) led to isolation of (R,E)-1-benzyl-2-(1-propenyl)piperidine in 99% yield with 96% ee, consistent with the net syn addition of the amine relative to the departing hydroxyl group.

Mukherjee, Paramita; Widenhoefer, Ross A.

2012-01-01

460

Synthesis of heteroarylated polyfluorobiphenyls via palladium-catalyzed sequential sp2 C-H bonds functionalizations.  

PubMed

The higher reactivity of C5-H bonds of heteroarenes as compared to C-H bonds of bromopolyfluorobenzenes for palladium-catalyzed direct arylation allows the selective synthesis of the polyfluoroaryl-heteroarenes in moderate to high yields, without C-H bond functionalization of the polyfluorobenzene ring. In most cases, low loading of Pd(OAc)2 catalyst (0.5-1 mol %) was employed. Then, from these heteroarylated polyfluorobenzenes, the palladium-catalyzed C-H bond functionalization of the polyfluorobenzene ring allows the synthesis of heteroarylated polyfluorobiphenyls. PMID:23445271

Yan, Tao; Chen, Lu; Bruneau, Christian; Dixneuf, Pierre H; Doucet, Henri

2013-03-13