The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Kotohiro Nomura - One of the best experts on this subject based on the ideXlab platform.
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Notable Effect of Fluoro Substituents in the Imino Group in Ring-Opening Polymerization of ε-Caprolactone by Al Complexes Containing Phenoxyimine Ligands
Organometallics, 2009Co-Authors: Naruhito Iwasa, Shohei Katao, Michiya Fujiki, Yoshiro Furukawa, Kotohiro NomuraAbstract:A series of Al complexes containing phenoxyimine ligands of the types R1(R2)Al[O-2-tBu-6-{(C6F5)N═CH}C6H3] [R1, R2 = Me, Me (1a); Et, Et (1b); Me, Cl (1c)] and Me2Al[O-2-tBu-6-(ArN═CH)C6H3] [Ar = 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a)] have been prepared and identified on the basis of NMR spectra and elemental analyses. Their structures were determined by X-ray crystallography, and these complexes fold a distorted tetrahedral geometry around Al. The ring-opening polymerizations (ROPs) of e-caprolactone (CL) using 1a−c in the presence of PhCH2OH proceeded efficiently in a living manner, and the propagation rates were somewhat influenced by the anionic donor ligand employed (Me, Et, or Cl). The catalytic activity by 1a−6a [Ar = C6H5 (5a), 2,6-Me2C6H3 (6a)]−PhCH2OH catalyst systems was strongly affected by the aromatic substituent (Ar) in the Imino Group, and placement of fluorine substituents especially in the ortho-position strongly affected the catalytic activity. The ROPs by 2a−6a were accompa...
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notable effect of fluoro substituents in the Imino Group in ring opening polymerization of e caprolactone by al complexes containing phenoxyimine ligands
Organometallics, 2009Co-Authors: Naruhito Iwasa, Shohei Katao, Michiya Fujiki, Yoshiro Furukawa, Kotohiro NomuraAbstract:A series of Al complexes containing phenoxyimine ligands of the types R1(R2)Al[O-2-tBu-6-{(C6F5)N═CH}C6H3] [R1, R2 = Me, Me (1a); Et, Et (1b); Me, Cl (1c)] and Me2Al[O-2-tBu-6-(ArN═CH)C6H3] [Ar = 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a)] have been prepared and identified on the basis of NMR spectra and elemental analyses. Their structures were determined by X-ray crystallography, and these complexes fold a distorted tetrahedral geometry around Al. The ring-opening polymerizations (ROPs) of e-caprolactone (CL) using 1a−c in the presence of PhCH2OH proceeded efficiently in a living manner, and the propagation rates were somewhat influenced by the anionic donor ligand employed (Me, Et, or Cl). The catalytic activity by 1a−6a [Ar = C6H5 (5a), 2,6-Me2C6H3 (6a)]−PhCH2OH catalyst systems was strongly affected by the aromatic substituent (Ar) in the Imino Group, and placement of fluorine substituents especially in the ortho-position strongly affected the catalytic activity. The ROPs by 2a−6a were accompa...
Janez Plavec - One of the best experts on this subject based on the ideXlab platform.
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structural dependence of isotope effects in 1h and 13c nuclear magnetic resonance spectra of the trans n benzylideneaniline Imino Group
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1998Co-Authors: Predrag Novak, Zlatko Meic, Dražen Vikictopic, Vilko Smrecki, Janez PlavecAbstract:Abstract Deuterium- and 15 N-induced isotope effects on 1 H and 13 C chemical shifts of the Imino moiety of 16 trans -N-benzylideneaniline (tBA) isotopomers were determined and analysed. These effects appear to be a sensitive probe of molecular conformation and its changes. All determined deuterium isotope effects on the Imino-proton are small and negative and are spread in the range from −0.88 ppb in 4- 2 H-tBA to −4.97 ppb in 2 H 10 -tBA. The effects on the Imino-carbon are either positive or negative and have much larger values. Negative sign of isotope effects is primarily governed by lone-pairs, while magnitude and non-additivity depend on the site of isotopic substitution, molecular conformation and distribution of rotamer populations. All 15 N isotope effects on both 1 H and 13 C chemical shifts are positive. A comparison of isotope effects in tBA with those in related isoelectronic compounds is made.
Naruhito Iwasa - One of the best experts on this subject based on the ideXlab platform.
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Notable Effect of Fluoro Substituents in the Imino Group in Ring-Opening Polymerization of ε-Caprolactone by Al Complexes Containing Phenoxyimine Ligands
Organometallics, 2009Co-Authors: Naruhito Iwasa, Shohei Katao, Michiya Fujiki, Yoshiro Furukawa, Kotohiro NomuraAbstract:A series of Al complexes containing phenoxyimine ligands of the types R1(R2)Al[O-2-tBu-6-{(C6F5)N═CH}C6H3] [R1, R2 = Me, Me (1a); Et, Et (1b); Me, Cl (1c)] and Me2Al[O-2-tBu-6-(ArN═CH)C6H3] [Ar = 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a)] have been prepared and identified on the basis of NMR spectra and elemental analyses. Their structures were determined by X-ray crystallography, and these complexes fold a distorted tetrahedral geometry around Al. The ring-opening polymerizations (ROPs) of e-caprolactone (CL) using 1a−c in the presence of PhCH2OH proceeded efficiently in a living manner, and the propagation rates were somewhat influenced by the anionic donor ligand employed (Me, Et, or Cl). The catalytic activity by 1a−6a [Ar = C6H5 (5a), 2,6-Me2C6H3 (6a)]−PhCH2OH catalyst systems was strongly affected by the aromatic substituent (Ar) in the Imino Group, and placement of fluorine substituents especially in the ortho-position strongly affected the catalytic activity. The ROPs by 2a−6a were accompa...
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notable effect of fluoro substituents in the Imino Group in ring opening polymerization of e caprolactone by al complexes containing phenoxyimine ligands
Organometallics, 2009Co-Authors: Naruhito Iwasa, Shohei Katao, Michiya Fujiki, Yoshiro Furukawa, Kotohiro NomuraAbstract:A series of Al complexes containing phenoxyimine ligands of the types R1(R2)Al[O-2-tBu-6-{(C6F5)N═CH}C6H3] [R1, R2 = Me, Me (1a); Et, Et (1b); Me, Cl (1c)] and Me2Al[O-2-tBu-6-(ArN═CH)C6H3] [Ar = 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a)] have been prepared and identified on the basis of NMR spectra and elemental analyses. Their structures were determined by X-ray crystallography, and these complexes fold a distorted tetrahedral geometry around Al. The ring-opening polymerizations (ROPs) of e-caprolactone (CL) using 1a−c in the presence of PhCH2OH proceeded efficiently in a living manner, and the propagation rates were somewhat influenced by the anionic donor ligand employed (Me, Et, or Cl). The catalytic activity by 1a−6a [Ar = C6H5 (5a), 2,6-Me2C6H3 (6a)]−PhCH2OH catalyst systems was strongly affected by the aromatic substituent (Ar) in the Imino Group, and placement of fluorine substituents especially in the ortho-position strongly affected the catalytic activity. The ROPs by 2a−6a were accompa...
Nils G Walter - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics suggest multifunctionality of an adenine Imino Group in acid base catalysis of the hairpin ribozyme
RNA, 2009Co-Authors: Mark A Ditzler, Jiři Sponer, Nils G WalterAbstract:Despite numerous structural and biochemical investigations, the catalytic mechanism of hairpin ribozyme self-cleavage remains elusive. To gain insight into the coupling of active site dynamics with activity of this small catalytic RNA, we analyzed a total of ;300 ns of molecular dynamics (MD) simulations. Our simulations predict improved global stability for an in vitro selected ‘‘gain of function’’ mutation, which is validated by native gel electrophoretic mobility shift assay. We observe that active site nucleobases and water molecules stabilize a geometry favorable to catalysis through a dynamic hydrogen bonding network. Simulations in which A38 is unprotonated show its N1 move into close proximity of the active site 29-OH, indicating that A38 may act as a general base during cleavage, a role that has generally been discounted due to the longer distances observed in crystal structures involving inactivating substrate analogs. By contrast, simulations in which N1 of A38 is protonated place N1 in close proximity to the 59-oxygen leaving Group, which supports the proposal that A38 serves as a general acid. In analogy to protein enzymes, we discuss a plausible mechanism in which A38 acts bifunctionally and shuttles a proton directly from the 29-OH to the 59-oxygen. Furthermore, our simulations suggest an important role for protonation of N1 of A38 in promoting a favorable geometry similar to that observed in transition-state analog crystal structures, and support previously proposed roles of A38, G8, and long residency water molecules in transition-state stabilization.
Joseph E Wedekind - One of the best experts on this subject based on the ideXlab platform.
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identification of an Imino Group indispensable for cleavage by a small ribozyme
Journal of the American Chemical Society, 2009Co-Authors: Robert C Spitale, Rosaria Volpini, M G Heller, J Krucinska, Gloria Cristalli, Joseph E WedekindAbstract:The hairpin ribozyme is a small, noncoding RNA (ncRNA) that catalyzes a site-specific phosphodiester bond cleavage reaction. Prior biochemical and structural analyses pinpointed the amidine moiety of base Ade38 as a key functional Group in catalysis, but base changes designed to probe function resulted in localized misfolding of the active site. To define the requirements for chemical activity using a conservative modification, we synthesized and incorporated N1-deazaadenosine into the full-length ribozyme construct. This single-atom variant severely impairs activity, although the active-site fold remains intact in the accompanying crystal structures. The results demonstrate the essentiality of the Imino moiety as well as the importance of its interaction with the substrate in the precatalytic and transition-state conformations. This work demonstrates the efficacy of single-atom approaches in the analysis of ncRNA structure−function relationships.
