Home – Home – Jornals – Journal of Structural Chemistry 2009 number 1

In this paper extensive systematic computational study has been carried out to justify hydrogen bonding interactions and its influence on the oxygen, nitrogen and hydrogen NQR and NMR parameters of the anhydrous and monohydrated guanine crystal structures at two different levels, B3LYP and MP2, using 6-311++G** and D95** basis sets. These theoretical data have been compared with experimental NMR and NQR measurements. For further investigation, results of cluster calculations have been compared with that of a single molecule. Our theoretical NQR and NMR parameters of ¹⁷O, ¹⁵N and ²H atoms of anhydrous and monohydrated guanine exhibited extreme sensitivity to electron distribution around mentioned nuclei caused by cooperative influences of various types of hydrogen bonding interactions. Fortunately, our calculated isotropic shielding values and CS tensors for the ¹⁷O and ¹⁵N nuclei as well as obtained ¹⁴N-NQR parameters are in excellent agreement with experimental data. Therefore, we can undoubtedly conclude that for anhydrous and monohydrated guanine tetrameric clusters including intermolecular interactions, our theoretical estimates are in better agreement with observed experimental values than those in which these interactions have been ignored.