Investigation of the effects of ionic hydrogen bonds (C=O-•••H-C and +N-H•••-O=C) in crystalline DL-proline by ab initio and DFT calculated NQR parameters

In this paper, we have calculated the nuclear quadrupole resonance (NQR) parameters of the quadrupole nuclei involved in the hydrogen bonds (C=O-center dot center dot center dot H-C and N+-H center dot center dot center dot O-=C in the monomer and pentameric cluster of DL-proline by HF and B3LYP methods and basis sets of 6-311+G* and 6-311++G**. These computations are performed on the basis of X-ray diffraction structural data of DL-proline. The results indicate that the calculations including hydropen-bonding (HB) interactions (in pentamer) are in better agreement with the experimental data than those in which these interactions are neglected (in monomer). The quantum chemical calculations show that the intermolecular hydrogen-bonding interactions play an important role in determination of the NQR parameters of N-14, H-2 of NH(2)(+)groupand O-17. (c) 2007 Elsevier B.V. All rights reserved.