Stephanie Mabry - Determination of the Activation Volume of the Uncatalyzed Hydrogen Exchange Reaction between N-Methylacetamide and Water

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  Publication Details (including relevant citation   information):

  S. A. Mabry, B.-S. Lee, T. Zheng, and J. Jonas, J. Amer. Chem.   Soc., 1996, 118, 8887-8890


  The amide−water hydrogen exchange rates of the individual   backbone amide protons are very sensitive to the local   environment of the protons and can be used to probe fluctuations   in the local conformations of proteins. Hydrogen exchange between   N-methylacetamide (NMA) and water is important in that   it serves as a model for the amide−water hydrogen exchange in   peptides and proteins. The rate constants for amide−water   hydrogen exchange between 16 mol % NMA and water at 66 °C were   measured at pressures ranging from 1 bar to 5 kbar at three   different pH values using the NMR magnetization transfer   technique, and the apparent activation volumes of hydrogen   exchange were obtained at each pH. The activation volume of the   acid-catalyzed hydrogen exchange reaction was calculated to be   +1.7 cm3 mol-1, and the activation volume   of the base-catalyzed hydrogen exchange reaction was calculated   to be +11.0 cm3 mol-1. The hydrogen   exchange rate constants were also measured as a function of   concentration and pH at ambient pressure at 66 °C so that the   rate constants of the acid-, base-, and uncatalyzed hydrogen   exchange reactions could be found. With these values, the   activation volume of the uncatalyzed hydrogen exchange reaction   was calculated to be equal to −9.0 cm3  mol-1. This quantity has not been previously   determined and is required in hydrogen exchange studies of   peptides and proteins at pressures above ambient pressure.

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