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|Title:||Liquid hot NAGMA cooled to 0.4 K: Benchmark thermochemistry of a gas-phase peptide|
|Citation:||Journal of Physical Chemistry A, 2014; 118(41):9692-9700|
|Publisher:||American Chemical Society|
|Christopher M. Leavitt, Kevin B. Moore III, Paul L. Raston, Jay Agarwal, Grant H. Moody, Caitlyne C. Shirley, Henry F. Schaefer III, and Gary E. Douberly|
|Abstract:||Vibrational spectroscopy and helium nanodroplet isolation are used to determine the gas-phase thermochemistry for isomerization between conformations of the model dipeptide, N-acetylglycine methylamide (NAGMA). A two-stage oven source is implemented to produce a gas-phase equilibrium distribution of NAGMA conformers, which is preserved when individual molecules are captured and cooled to 0.4 K by He nanodroplets. With polarization spectroscopy, the IR spectrum in the NH stretch region is assigned to a mixture of two conformers having intramolecular hydrogen bonds composed of either five- or seven-membered rings, C5 and C7, respectively. The C5 to C7 interconversion enthalpy and entropy, obtained from a van't Hoff analysis, are -4.52 ± 0.12 kJ/mol and -12.4 ± 0.2 J/(mol · K), respectively. The experimental thermochemistry is compared to high-level electronic structure theory computations.|
|Keywords:||Helium; Gases; Peptides; Spectrum Analysis; Hydrogen Bonding; Nanotechnology; Vibration; Thermodynamics; Entropy; Models, Molecular|
|Rights:||© 2014 American Chemical Society|
|Appears in Collections:||Physics publications|
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