The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Irene C M Kwan - One of the best experts on this subject based on the ideXlab platform.
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probing hydrogen bonding and ion Carbonyl interactions by solid state 17o nmr spectroscopy g ribbon and g quartet
Journal of the American Chemical Society, 2007Co-Authors: Irene C M KwanAbstract:We report solid-state 17O NMR determination of the 17O NMR tensors for the keto Carbonyl Oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2‘,3‘,5‘-O-triacetyl-[6-17O]guanosine (G2). In G1·2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6···H−N2 and N7···H−N7 hydrogen bonds in a zigzag fashion. In addition, the keto Carbonyl Oxygen O6 is also weakly hydrogen-bonded to two water molecules of hydration. The experimental 17O NMR tensors determined for the two independent molecules in the asymmetric unit of G1·2H2O are: Molecule A, CQ = 7.8 ± 0.1 MHz, ηQ = 0.45 ± 0.05, δiso = 263 ± 2, δ11 = 460 ± 5, δ22 = 360 ± 5, δ33 = −30 ± 5 ppm; Molecule B, CQ = 7.7 ± 0.1 MHz, ηQ = 0.55 ± 0.05, δiso = 250 ± 2, δ11 = 440 ± 5, δ22 = 340 ± 5, δ33 = −30 ± 5 ppm. In G1/K+ gel, guanosine molecules form extensively stacking G-quartets. In each G-quartet, four guanine bases are linked together by four pairs of O6···H−N1 and N7···H−N2 hydro...
And Shuan Dong - One of the best experts on this subject based on the ideXlab platform.
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solid state 17o nmr investigation of the Carbonyl Oxygen electric field gradient tensor and chemical shielding tensor in amides
Journal of the American Chemical Society, 2000Co-Authors: Kazuhiko Yamada, And Shuan DongAbstract:We have presented a systematic experimental and theoretical investigation of the Carbonyl Oxygen electric-field-gradient (EFG) tensor and chemical shielding (CS) tensor in crystalline amides. Three 17O-labled secondary amides, R1C[17O]-NHR2, have been synthesized: benzanilide (1), N-methylbenzamide (2), and acetanilide (3). Analysis of 17O magic-angle spinning (MAS) and stationary NMR spectra yields not only the magnitude but also the orientation of the Carbonyl 17O EFG and CS tensors. For compounds 1−3, the Carbonyl 17O quadrupolar coupling constant (QCC) and the span of the chemical shift tensor are found to be in the range of 8.5−8.97 MHz and 560−630 ppm, respectively. The largest 17O EFG component lies in the amide plane and is perpendicular to the CO bond, whereas the smallest component is perpendicular to the N−CO plane. For the Carbonyl 17O CS tensor, the principal component with the largest shielding, δ33, is perpendicular to the amide plane, and the tensor component corresponding to the least sh...
Kazuhiko Yamada - One of the best experts on this subject based on the ideXlab platform.
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solid state 17o nmr investigation of the Carbonyl Oxygen electric field gradient tensor and chemical shielding tensor in amides
Journal of the American Chemical Society, 2000Co-Authors: Kazuhiko Yamada, And Shuan DongAbstract:We have presented a systematic experimental and theoretical investigation of the Carbonyl Oxygen electric-field-gradient (EFG) tensor and chemical shielding (CS) tensor in crystalline amides. Three 17O-labled secondary amides, R1C[17O]-NHR2, have been synthesized: benzanilide (1), N-methylbenzamide (2), and acetanilide (3). Analysis of 17O magic-angle spinning (MAS) and stationary NMR spectra yields not only the magnitude but also the orientation of the Carbonyl 17O EFG and CS tensors. For compounds 1−3, the Carbonyl 17O quadrupolar coupling constant (QCC) and the span of the chemical shift tensor are found to be in the range of 8.5−8.97 MHz and 560−630 ppm, respectively. The largest 17O EFG component lies in the amide plane and is perpendicular to the CO bond, whereas the smallest component is perpendicular to the N−CO plane. For the Carbonyl 17O CS tensor, the principal component with the largest shielding, δ33, is perpendicular to the amide plane, and the tensor component corresponding to the least sh...
Nan Zheng - One of the best experts on this subject based on the ideXlab platform.
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iridium catalyzed highly regioselective azide ynamide cycloaddition to access 5 amido fully substituted 1 2 3 triazoles under mild air aqueous and bioorthogonal conditions
Organic Letters, 2017Co-Authors: Wangze Song, Nan ZhengAbstract:A highly regioselective method to access 5-amido fully substituted 1,2,3-triazoles by iridium-catalyzed azide-ynamide cycloaddition under mild, air, aqueous, and bioorthogonal conditions is reported. The excellent regioselectivities may derive from the strong coordination between the Carbonyl Oxygen of ynamide and the π-acidic iridium. Since the iridium ion is insensitive to Oxygen/water and exhibits low cytotoxicity, it could catalyze this reaction in both organic and biological environments efficiently. Preparation in gram-scale and application in carbohydrates highlight this method.
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Iridium-Catalyzed Highly Regioselective Azide–Ynamide Cycloaddition to Access 5‑Amido Fully Substituted 1,2,3-Triazoles under Mild, Air, Aqueous, and Bioorthogonal Conditions
2017Co-Authors: Wangze Song, Nan ZhengAbstract:A highly regioselective method to access 5-amido fully substituted 1,2,3-triazoles by iridium-catalyzed azide–ynamide cycloaddition under mild, air, aqueous, and bioorthogonal conditions is reported. The excellent regioselectivities may derive from the strong coordination between the Carbonyl Oxygen of ynamide and the π-acidic iridium. Since the iridium ion is insensitive to Oxygen/water and exhibits low cytotoxicity, it could catalyze this reaction in both organic and biological environments efficiently. Preparation in gram-scale and application in carbohydrates highlight this method
Adinath Majee - One of the best experts on this subject based on the ideXlab platform.
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Vinylation of Carbonyl Oxygen in 4-Hydroxycoumarin: Synthesis of Heteroarylated Vinyl Ethers
Synthesis, 2019Co-Authors: Rana Chatterjee, Sougata Santra, Grigory V. Zyryanov, Adinath MajeeAbstract:The unique nucleophilic character of the Carbonyl Oxygen of 4-hydroxy coumarin has been observed by the BF3·OEt2 catalyzed reaction of 4-hydroxycoumarin and alkynes. The reactions of 4-hydroxycoumarin and substituted 4-hydroxycoumarin with various terminal alkynes have been studied. In case of internal alkyne (prop-1-yn-1-ylbenzene), the reaction with 4-hydroxycoumarin led to the corresponding product with an E/Z ratio of 3:1. This protocol is operationally very simple and has much potential for the synthesis of heteroarylated vinyl ethers from basic chemicals.