Encapsulation of Protonated Diamines in a Water-Soluble Chiral, Supramolecular Assembly Allows for Measurement of Hydrogen-Bond Breaking Followed by Nitrogen Inversion/Rotation (NIR)

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Amine nitrogen inversion, difficult to observe in aqueous solution, is followed in a chiral, supramolecular host molecule with purely-rotational T-symmetry that reduces the local symmetry of encapsulated monoprotonated diamines and enables the observation and quantification of {Delta}G{double_dagger} for the combined hydrogen-bond breaking and nitrogen inversion rotation (NIR) process. Free energies of activation for the combined hydrogen-bond breaking and NIR process inside of the chiral assembly were determined by the NMR coalescence method. Activation parameters for ejection of the protonated amines from the assembly confirm that the NIR process responsible for the coalescence behavior occurs inside of the assembly rather than ... continued below

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Meux, Susan C.; Pluth, Michael D.; Bergman, Robert G. & Raymond, Kenneth N. September 19, 2007.

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Amine nitrogen inversion, difficult to observe in aqueous solution, is followed in a chiral, supramolecular host molecule with purely-rotational T-symmetry that reduces the local symmetry of encapsulated monoprotonated diamines and enables the observation and quantification of {Delta}G{double_dagger} for the combined hydrogen-bond breaking and nitrogen inversion rotation (NIR) process. Free energies of activation for the combined hydrogen-bond breaking and NIR process inside of the chiral assembly were determined by the NMR coalescence method. Activation parameters for ejection of the protonated amines from the assembly confirm that the NIR process responsible for the coalescence behavior occurs inside of the assembly rather than by a guest ejection/NIR/re-encapsulation mechanism. For one of the diamines, N,N,N{prime},N{prime}-tetramethylethylenediamine (TMEDA), the relative energy barriers for the hydrogen-bond breaking and NIR process were calculated at the G3(MP2)//B3LYP/6-31++G(d,p) level of theory, and these agreed well with the experimental data.

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  • Journal Name: Journal of the American Chemical Society; Journal Volume: 130; Related Information: Journal Publication Date: 2008

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  • Report No.: LBNL-278E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 928967
  • Archival Resource Key: ark:/67531/metadc894685

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  • September 19, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Sept. 30, 2016, 6:27 p.m.

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Meux, Susan C.; Pluth, Michael D.; Bergman, Robert G. & Raymond, Kenneth N. Encapsulation of Protonated Diamines in a Water-Soluble Chiral, Supramolecular Assembly Allows for Measurement of Hydrogen-Bond Breaking Followed by Nitrogen Inversion/Rotation (NIR), article, September 19, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc894685/: accessed August 16, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.