title: The conformational behavior and H-bond structure of asparagine: a theoretical and experimental matrix-isolation FT-IR study.
abstract: Due to the high importance of the structural properties of peptides, the conformational behavior of one of their elementary building blocks, asparagine, has been investigated in this work. Matrix-isolation FT-IR spectroscopy is a suitable technique to investigate the intrinsic properties of small molecules. Asparagine has been subjected to matrix-isolation FT-IR spectroscopy supported with DFT and MP2 calculations. DFT optimization of asparagine resulted in 10 stable conformations with ∆E(DFT)<10 kJ.mol(-1). Compared to a previous study, one new conformation has been revealed. Further optimization at the MP2/6-31++G** level resulted in seven conformations with ∆E(MP)<10 kJ.mol(-1). A conformation containing the three intramolecular H-bonds, i.e. C=O(sc)…HN(bb), C=O(bb)…HN(sc) and OH(bb)…N(bb) appeared to be the most stable one at both levels despite the large negative entropy contribution due to these 3 H-bonds. At the sublimation temperature of 353 K, the DFT method predicts four and the MP2 method six conformations to be present in the experimental matrix-isolation spectrum. These conformations have different intramolecular H-bonds, which has allowed to identify at least 4 low energy conformations in the FT-IR spectrum. Detailed comparison between theory and experiment resulted in a mean frequency deviation of 7.6 cm(-1).
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200 F, B-3001 Leuven, Belgium. boeckx@hotmail.com
authors.forename: Bram
authors.initials: B
authors.lastname: Boeckx
authors.forename: Guido
authors.initials: G
authors.lastname: Maes
mesh_terms: D001216:Asparagine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
chemical_list: D001216:Asparagine