The Experts below are selected from a list of 8361 Experts worldwide ranked by ideXlab platform
Zhaomin Hou - One of the best experts on this subject based on the ideXlab platform.
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Cooperative Trimerization of Carbon Monoxide by Lithium and Samarium Boryls.
Journal of the American Chemical Society, 2017Co-Authors: Baoli Wang, Luo, Masayoshi Nishiura, Yi Luo, Zhaomin HouAbstract:The conversion of carbon monoxide (CO) to hydrocarbons and oxygenates on industrial solid catalysts (the Fischer–Tropsch reaction) largely relies on the cooperation of heteromultimetallic active sites composed of main group (such as alkali) and transition metals, but the mechanistic details have not been fully understood at the molecular level. Here we report the cooperative Trimerization of CO by molecular lithium and samarium boryl complexes. We have found that, in the coexistence of a samarium boryl complex and a lithium boryl complex, the Trimerization of CO selectively occurred to give a diborylallenetriolate skeleton “BC(O)C(O)C(O)B”, in sharp contrast with the reaction of CO with either the lithium or the samarium boryl compound alone. The 13C-labeled experiments and computational studies have revealed that the CO Trimerization reaction took place exclusively by coupling of a samarium boryl oxycarbene species, which was generated by insertion of one molecule of CO into the samarium–boryl bond, with...
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cooperative Trimerization of carbon monoxide by lithium and samarium boryls
Journal of the American Chemical Society, 2017Co-Authors: Baoli Wang, Masayoshi Nishiura, Yi Luo, Gen Luo, Zhaomin HouAbstract:The conversion of carbon monoxide (CO) to hydrocarbons and oxygenates on industrial solid catalysts (the Fischer-Tropsch reaction) largely relies on the cooperation of heteromultimetallic active sites composed of main group (such as alkali) and transition metals, but the mechanistic details have not been fully understood at the molecular level. Here we report the cooperative Trimerization of CO by molecular lithium and samarium boryl complexes. We have found that, in the coexistence of a samarium boryl complex and a lithium boryl complex, the Trimerization of CO selectively occurred to give a diborylallenetriolate skeleton "BC(O)C(O)C(O)B", in sharp contrast with the reaction of CO with either the lithium or the samarium boryl compound alone. The 13C-labeled experiments and computational studies have revealed that the CO Trimerization reaction took place exclusively by coupling of a samarium boryl oxycarbene species, which was generated by insertion of one molecule of CO into the samarium-boryl bond, with a lithium ketenolate species formed by insertion of two molecules of CO into the lithium-boryl bond. These results offer unprecedented insight into CO oligomerization promoted by heteromultimetallic components and may help better understand the industrial F-T process and guide designing new catalysts.
John E. Bercaw - One of the best experts on this subject based on the ideXlab platform.
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Ethylene and alpha olefin Trimerization and tandem Trimerization/polymerization of ethylene
2016Co-Authors: John E. Bercaw, Jay A. Labinger, Aaron Sattler, Dinesh C. Aluthge, Mamdouh Al HarthiAbstract:Mechanistic studies of homogeneous chromium- and titanium- catalyzed Trimerization of ethylene will be described. These studies point to a principal pathway for catalyst decompn. for the Fujita titanium system- conproportionation to Ti(III). Accordingly, a silica /MAO supported version has been prepd. and shown to give greater than 10 times higher turnover no. as compared with the homogeneous version under the same conditions. The high activity of the supported Fujita system allows for alpha olefin Trimerization to largely two trimers. Tandem and supported- tandem ethylene polymn. and Trimerization catalysts yield linear low d. polyethylene from an ethylene-only stock.
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Enhanced Productivity of a Supported Olefin Trimerization Catalyst
ACS Catalysis, 2015Co-Authors: Aaron Sattler, Jay A. Labinger, Dinesh C. Aluthge, Jay R. Winkler, John E. BercawAbstract:Treatment of dry silica with methylaluminoxane (MAO) followed by (FI)TiCl3 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2′-(2″-methoxyphenyl)anilinato) gives a heterogeneous supported ethylene Trimerization catalyst, s(FI)Ti, which exhibits productivity more than an order of magnitude higher than its homogeneous analogues. This increase in productivity is attributed to a decreased rate of catalyst decomposition, a process that is proposed to occur via comproportionation to an inactive TiIII species; immobilization retards this process. In addition, s(FI)Ti catalyzes Trimerization of α-olefins with high selectivity. Based on regioisomer distributions, catalysis by s(FI)Ti involves the same active species as the previously reported homogeneous systems (FI)TiR2Me/B(C6F5)3 (R = Me, CH2SiMe3, CH2CMe3).
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Upgrading light olefins by Trimerization catalysis
2014Co-Authors: Aaron Sattler, Jay A. Labinger, Jay R. Winkler, Harry B. Gray, John E. BercawAbstract:Activation of a (phenoxy-imine) titanium tri-Me complex with one equiv. of B(C_6F_5)_3 effects the catalytic Trimerization of ethylene. Stoichiometric activation with B(C_6F_5)_3 allows for mechanistic studies to be conducted, which give insight into catalyst initiation, Trimerization, and decompn., and the relative rates of these processes. In addn. to ethylene, α-olefins are oligomerized with high selectivity for trimers (> 95%), of which approx. 85% are one regioisomer.
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highly selective olefin Trimerization catalysis by a borane activated titanium trimethyl complex
Organometallics, 2013Co-Authors: Aaron Sattler, Jay A. Labinger, John E. BercawAbstract:Reaction of a trimethyl titanium complex, (FI)TiMe3 (FI = phenoxy-imine), with 1 equiv of B(C6F5)3 gives [(FI)TiMe2][MeB(C6F5)3], an effective precatalyst for the selective Trimerization of ethylene. Mechanistic studies indicate that catalyst initiation involves generation of an active TiII species by olefin insertion into a Ti–Me bond, followed by β-H elimination and reductive elimination of methane, and that initiation is slow relative to Trimerization. (FI)TiMe3/B(C6F5)3 also leads to a competent catalyst for the oligomerization of α-olefins, displaying high selectivity for trimers (>95%), approximately 85% of which are one regioisomer. This catalyst system thus shows promise for selectively converting light α-olefins into transportation fuels and lubricants.
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mechanistic studies of olefin and alkyne Trimerization with chromium catalysts deuterium labeling and studies of regiochemistry using a model chromacyclopentane complex
Journal of the American Chemical Society, 2007Co-Authors: Theodor Agapie, Jay A. Labinger, John E. BercawAbstract:A system for catalytic Trimerization of ethylene utilizing chromium(III) precursors supported by diphosphine ligand PNP^(O4) = (o-MeO−C_6H_4)_2PN(Me)P(o-MeO−C_6H_4)_2 has been investigated. The mechanism of the olefin Trimerization reaction was examined using deuterium labeling and studies of reactions with α-olefins and internal olefins. A well-defined chromium precursor utilized in this studies is Cr(PNP^(O4))(o,o‘-biphenyldiyl)Br. A cationic species, obtained by halide abstraction with NaB[C_6H_3(CF_3)_2]_4, is required for catalytic turnover to generate 1-hexene from ethylene. The initiation byproduct is vinylbiphenyl; this is formed even without activation by halide abstraction. Trimerization of 2-butyne is accomplished by the same cationic system but not by the neutral species. Catalytic Trimerization, with various (PNP^(O4))Cr precursors, of a 1:1 mixture of C_2D_4 and C_2H_4 gives isotopologs of 1-hexene without H/D scrambling (C_6D_(12), C_6D_8H_4, C_6D_4H_8, and C_6H_(12) in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. Using a SHOP catalyst to perform the oligomerization of a 1:1 mixture of C_2D_4 and C_2H_4 leads to the generation of a broader distribution of 1-hexene isotopologs, consistent with a Cossee-type mechanism for 1-hexene formation. The ethylene Trimerization reaction was further studied by the reaction of trans-, cis-, and gem-ethylene-d_2 upon activation of Cr(PNP^(O4))(o,o‘-biphenyldiyl)Br with NaB[C_6H_3(CF_3)_2]_4. The Trimerization of cis- and trans-ethylene-d_2 generates 1-hexene isotopomers having terminal CDH groups, with an isotope effect of 3.1(1) and 4.1(1), respectively. These results are consistent with reductive elimination of 1-hexene from a putative Cr(H)[(CH_2)_4CH═CH_2] occurring much faster than a hydride 2,1-insertion or with concerted 1-hexene formation from a chromacycloheptane via a 3,7-H shift. The Trimerization of gem-ethylene-d2 has an isotope effect of 1.3(1), consistent with irreversible formation of a chromacycloheptane intermediate on route to 1-hexene formation. Reactions of olefins with a model of a chromacyclopentane were investigated starting from Cr(PNP^(O4))(o,o‘-biphenyldiyl)Br. α-Olefins react with cationic biphenyldiyl chromium species to generate products from 1,2-insertion. A study of the reaction of 2-butenes indicated that β-H elimination occurs preferentially from the ring CH rather than exo-CH bond in the metallacycloheptane intermediates. A study of coTrimerization of ethylene with propylene correlates with these findings of regioselectivity. Competition experiments with mixtures of two olefins indicate that the relative insertion rates generally decrease with increasing size of the olefins.
Patrick W.k. Lee - One of the best experts on this subject based on the ideXlab platform.
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Co-translational Trimerization of the reovirus cell attachment protein.
The EMBO journal, 1996Co-Authors: Ross Gilmore, Gustavo Leone, Matthew C. Coffey, Kevin G. Mclure, Patrick W.k. LeeAbstract:The reovirus cell attachment protein, sigma1, is a trimer with a 'lollipop' structure. Recent findings indicate that the N-terminal fibrous tail and the C-terminal globular head each possess a distinct Trimerization domain. The region responsible for N-terminal Trimerization (formation of a triple alpha-helical coiled-coil) is located at the N-terminal one-third of sigma1. In this study, we investigated the temporality and ATP requirement of this Trimerization event in the context of sigma1 biogenesis. In vitro co-synthesis of the full-length (FL) and a C-terminally truncated (d44) sigma1 protein revealed a preference for homotrimer over heterotrimer formation, suggesting that assembly at the N-terminus occurs co-translationally. This was corroborated by the observation that polysome-associated sigma1 chains were trimeric as well as monomeric. Truncated proteins (d234 and d294) with C-terminal deletions exceeding half the length of sigma1 were found to trimerize post-translationally. This Trimerization did not require ATP since it proceeded normally in the presence of apyrase. In contrast, formation of stable FL sigma1 trimers was inhibited by apyrase treatment. Collectively, our data suggest that assembly of nascent sigma1 chains at the N-terminus is intrinsically ATP independent, and occurs co-translationally when the ribosomes have traversed past the midpoint of the mRNA.
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C-terminal Trimerization, but not N-terminal Trimerization, of the reovirus cell attachment protein Is a posttranslational and Hsp70/ATP-dependent process.
The Journal of biological chemistry, 1996Co-Authors: Gustavo Leone, Roy Duncan, Matthew C. Coffey, Ross Gilmore, Lloyd Maybaum, Patrick W.k. LeeAbstract:Abstract The C-terminal globular head of the lollipop-shaped 1 protein of reovirus is responsible for interaction with the host cell receptor. Like the N-terminal fibrous tail, it has its own Trimerization domain. Whereas N-terminal Trimerization (formation of a triple α-helical coiled coil) occurs at the level of polysomes (i.e. cotranslationally) and is ATP-independent, C-terminal Trimerization is a posttranslational event that requires ATP. Coprecipitation experiments using anti-Hsp70 antibodies and truncated 1 proteins synthesized in vitro revealed that only regions downstream of the N-terminal α-helical coiled coil were associated with Hsp70. Hsp70 was also found to be associated with nascent 1 chains on polysomes as well as with immature postribosomal 1 trimers (hydra-like intermediates with assembled N termini and unassembled C termini). These latter structures were true intermediates in the 1 biogenetic pathway since they could be chased into mature 1 trimers with the release of Hsp70. Thus, unlike N-terminal Trimerization, C-terminal Trimerization is Hsp70- and ATP-dependent. The involvement of two mechanistically distinct oligomerization events for the same molecule, one cotranslational and one posttranslational, may represent a common approach to the generation of oligomeric proteins in the cytosol.
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Trimerization of the reovirus cell attachment protein (σI) induces conformational changes in σI necessary for its cell-binding function
Virology, 1991Co-Authors: Gustavo Leone, Roy Duncan, Patrick W.k. LeeAbstract:Abstract The implications of reovirus σI protein Trimerization on its cell-binding function were investigated. Both monomeric and trimeric forms of σI were found to be present when full-length type 3 reovirus SI transcripts prepared in vitro were translated in rabbit reticulocyte lysates. Pulse-chase experiments demonstrated that monomers were precursors of trimers. However, only the trimeric form was capable of binding to cell surface receptors. Protease and antibody recognition analyses revealed significant structural differences between these two σI forms at both the N- and C-termini. Our results suggest that Trimerization of protein of is accompanied by extensive conformational changes necessary for its cell attachment function.
Baoli Wang - One of the best experts on this subject based on the ideXlab platform.
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Cooperative Trimerization of Carbon Monoxide by Lithium and Samarium Boryls.
Journal of the American Chemical Society, 2017Co-Authors: Baoli Wang, Luo, Masayoshi Nishiura, Yi Luo, Zhaomin HouAbstract:The conversion of carbon monoxide (CO) to hydrocarbons and oxygenates on industrial solid catalysts (the Fischer–Tropsch reaction) largely relies on the cooperation of heteromultimetallic active sites composed of main group (such as alkali) and transition metals, but the mechanistic details have not been fully understood at the molecular level. Here we report the cooperative Trimerization of CO by molecular lithium and samarium boryl complexes. We have found that, in the coexistence of a samarium boryl complex and a lithium boryl complex, the Trimerization of CO selectively occurred to give a diborylallenetriolate skeleton “BC(O)C(O)C(O)B”, in sharp contrast with the reaction of CO with either the lithium or the samarium boryl compound alone. The 13C-labeled experiments and computational studies have revealed that the CO Trimerization reaction took place exclusively by coupling of a samarium boryl oxycarbene species, which was generated by insertion of one molecule of CO into the samarium–boryl bond, with...
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cooperative Trimerization of carbon monoxide by lithium and samarium boryls
Journal of the American Chemical Society, 2017Co-Authors: Baoli Wang, Masayoshi Nishiura, Yi Luo, Gen Luo, Zhaomin HouAbstract:The conversion of carbon monoxide (CO) to hydrocarbons and oxygenates on industrial solid catalysts (the Fischer-Tropsch reaction) largely relies on the cooperation of heteromultimetallic active sites composed of main group (such as alkali) and transition metals, but the mechanistic details have not been fully understood at the molecular level. Here we report the cooperative Trimerization of CO by molecular lithium and samarium boryl complexes. We have found that, in the coexistence of a samarium boryl complex and a lithium boryl complex, the Trimerization of CO selectively occurred to give a diborylallenetriolate skeleton "BC(O)C(O)C(O)B", in sharp contrast with the reaction of CO with either the lithium or the samarium boryl compound alone. The 13C-labeled experiments and computational studies have revealed that the CO Trimerization reaction took place exclusively by coupling of a samarium boryl oxycarbene species, which was generated by insertion of one molecule of CO into the samarium-boryl bond, with a lithium ketenolate species formed by insertion of two molecules of CO into the lithium-boryl bond. These results offer unprecedented insight into CO oligomerization promoted by heteromultimetallic components and may help better understand the industrial F-T process and guide designing new catalysts.
Ludmilla Sissoeff - One of the best experts on this subject based on the ideXlab platform.
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stable Trimerization of recombinant rabies virus glycoprotein ectodomain is required for interaction with the p75ntr receptor
Journal of General Virology, 2005Co-Authors: Ludmilla Sissoeff, Mohamed Mousli, Patrick England, Christine TuffereauAbstract:Native rabies virus glycoprotein (RVGvir) is a trimeric, membrane-anchored protein that has been shown to interact with the p75NTR neurotrophin receptor. In order to determine if the RVG trimeric oligomerization state is required for its binding with p75NTR, different soluble recombinant molecules containing the entire RVG ectodomain (RVGect) were expressed alone or fused at its C terminus to the Trimerization domain of the bacteriophage T4 fibritin, termed ‘foldon’. The oligomerization status of recombinant RVG was investigated using sedimentation in sucrose gradient and p75NTR binding assays. It was found that, in the absence of the fibritin foldon, recombinant RVGect forms unstable trimers that dissociate into monomers in a concentration-dependent manner. C-terminal fusion with the foldon induces stable RVG Trimerization, which is concentration-independent. Furthermore, the fibritin foldon maintains the native antigenic structure of the carboxy part of RVGect. Cell binding experiments showed that RVG Trimerization is required for efficient interaction with p75NTR. However, the exact mode of Trimerization appears unimportant, as trimeric recombinant RVGect (fused to the fibritin foldon) and RVGvir both recognize p75NTR with similar nanomolar affinities, as shown by surface plasmon resonance experiments. Altogether, these results show that the C-terminal fusion of the RVG ectodomain with the fibritin foldon is a powerful way to obtain a recombinant trimeric native-like structure of the p75NTR binding domain of RVG.
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Stable Trimerization of recombinant rabies virus glycoprotein ectodomain is required for interaction with the p75(NTR) receptor
Journal of General Virology, 2005Co-Authors: Ludmilla Sissoeff, Mohamed Mousli, Patrick England, Christine TufferauAbstract:Native rabies virus glycoprotein (RVGvir) is a trimeric, membrane-anchored protein that has been shown to interact with the p75(NTR) neurotrophin receptor. In order to determine if the RVG trimeric oligomerization state is required for its binding with p75(NTR), different soluble recombinant molecules containing the entire RVG ectodomain (RVGect) were expressed alone or fused at its C terminus to the Trimerization domain of the bacteriophage T4 fibritin, termed 'foldon'. The oligomerization status of recombinant RVG was investigated using sedimentation in sucrose gradient and p75(NTR) binding assays. It was found that, in the absence of the fibritin foldon, recombinant RVGect forms unstable trimers that dissociate into monomers in a concentration-dependent manner. C-terminal fusion with the foldon induces stable RVG Trimerization, which is concentration-independent. Furthermore, the fibritin foldon maintains the native antigenic structure of the carboxy part of RVGect. Cell binding experiments showed that RVG Trimerization is required for efficient interaction with p75(NTR). However, the exact mode of Trimerization appears unimportant, as trimeric recombinant RVGect (fused to the fibritin foldon) and RVGvir both recognize p75(NTR) with similar nanomolar affinities, as shown by surface plasmon resonance experiments. Altogether, these results show that the C-terminal fusion of the RVG ectodomain with the fibritin foldon is a powerful way to obtain a recombinant trimeric native-like structure of the p75(NTR) binding domain of RVG.
