| The intermolecular interactions of three different binary systems were investigated with computational quantum chemical methods respectively,to predict the geometries and take the systematically analysis to weak interaction about the principle and mechanism.First, the B3LYP/6-311+G* method was performed on complexes of guanine with acrylamide, and nine stable configurations were obtained with no real frequencies. Then the B3LYP/6-311+G* and MP2/6-31+G* methods were used to study the complexes between cytosine and acrylamide. The structures, binding energy, charge transfer and topological property of the complexes were calculated. The results indicated the presence of CH…O, CH…N,NH…O and NH…N hydrogen bonds between guanine with acrylamide, cytosine and acrylamide in these conformers and the interaction energies of hydrogen bonding of the systems decreased in the following sequence: A1 > A2 > A3 > A5 > A4 > A6> A7 > A8 > A9 (guanine-acrylamide system), A3 > A4 > A1 > A2 > A5 (cytosine -acrylamide system).Finally, we performed DFT calculation with 6-311+G* basis set on the hydrogen-bonded complexes between guanine and urea. The nearly linear NH…O contacts are stronger than a conventional hydrogen bond interaction with their H…O separation between 1.74 and 2.68 ?. Urea is a good hydrogen bond accepter and for N or O atom, it is a good hydrogen bond donor. Thus, stable complexes can formed between urea and guanine with hydrogen bonds. The hydrogen bonds'strength decreased in the following sequence: NH…O > NH…N > CH…O. According to the AIM and NBO analysises, hydrogen bond between guanine and urea is important and A5 is the most stable one.H-bonds interactions play an important role in supramolecular chemistry, especially in biological systems. As for supramolecular biological systems, the closely linear amide hydrogen bonds NH…O and NH…N strongly stabilize the complex. The weaker CH…O H-bonds are also discussed as significant interaction in biological systems.
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