Theoretical 13C chemical shift, 14N, and 2H quadrupole coupling- constant studies of hydrogen bonding in L-alanylglycine dipeptide

✍ Scribed by M. Tafazzoli; S. K. Amini

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 380 KB
• Volume: 46
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2185

✦ Synopsis

Abstract

^13^C chemical shieldings and ^14^N and ^2^H electric field gradient (EFG) tensors of L‐alanylglycine (L‐alagly) dipeptide were calculated at RHF/6–31 + + G** and B3LYP/6–31 + + G** levels of theory respectively. For these calculations a crystal structure of this dipeptide obtained from X‐ray crystallography was used. Atomic coordinates of different clusters containing several L‐alagly molecules were used as input files for calculations. These clusters consist of central and surrounding L‐alagly molecules, the latter forming short, strong, hydrogen bonds with the central molecule. Since the calculations did not converge for these clusters, the surrounding L‐alagly molecules were replaced by glycine molecules. In order to improve the accuracy of calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs), different geometry‐optimization strategies were applied for hydrogen nuclei. Agreement between calculated and experimental data confirms that our optimized coordinates for hydrogen nuclei are more accurate than those obtained by X‐ray diffraction. Copyright © 2008 John Wiley & Sons, Ltd.