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Conformational behavior and potential energy profile of gaseous histidine

Aliakbar Tehrani, Z ; Sharif University of Technology | 2010

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  1. Type of Document: Article
  2. DOI: 10.1016/j.theochem.2010.08.025
  3. Publisher: 2010
  4. Abstract:
  5. Histidine as a natural amino acid is found to be biologically important and is known to function as a nucleophile or enzyme co-factor, or in proton transfer process. The properties of gaseous aromatic amino acid histidine depend on the structural forms it may take in gas-phase. Ab initio method has been used to characterize the gas-phase conformer/tautomers of histidine. Wide range of possible structures for histidine was surveyed at the MM level, and then the geometries of the unique conformers were refined at the B3LYP/6-311++G (d,p) levels. At this theoretical level, 25 conformers were located for both tautomers of histidine i.e., His [NπH] and His [NτH]. The MM level provides a poor description of the relative energies. Calculations at the B3LYP/6-311++G (d,p) level represent a significant improvement. Ab initio dipole moments are reported for all the conformers/tautomers. The results are compared to previous studies of amino acids and are analyzed in terms of intramolecular hydrogen-bonding interactions and Newman projections. In addition, we calculated the infrared frequencies and intensities of the most stable structures in order to assist in the assignment of hydrogen-bonding. Furthermore, Ramachandran backbone potential energy surfaces (PES) of 25 conformers of His [NπH] and His [NτH] tautomers of histidine were considered. The stationary points characterizing the potential energy profile of the various conformers/tautomers of histidine were investigated by the same density functional theory B3LYP/6-311++G (d,p). Minima and transition states characterizing the energetic paths for the interconversion of various structures of histidine were explored in detail
  6. Keywords:
  7. Conformer ; DFT ; Histidine ; Potential energy profile ; Ramachandran backbone potential energy surfaces
  8. Source: Journal of Molecular Structure: THEOCHEM ; Volume 960, Issue 1-3 , November , 2010 , Pages 73-85 ; 01661280 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S0166128010005452