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1 2003

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Theoretical Study of the Interaction Between 2-Aminopyridine and 2-Aminopyrazine and Water

Chandra A., Zeegers-Huyskens Th.

Polish Journal of Chemistry

2003

Vol. 77 / nr 11

1649-1658

This work deals with a theoretical study of the interaction between one water molecule with 2-aminopyridine (2-NH2PYR) and 2-aminopyrazine (2-NH2PYZ). The optimized geometries, harmonic vibrational frequencies, binding energies, proton affinities of the heterocyclic nitrogen atom and the deprotonation enthalpies of the NH bonds are calculated by the DFT/B3LYP functional combined with the 6-31+G(d,p) basis set. The two complexes are cyclic. Complex formation results in a marked decrease of the pyramidal character of the amino group. The binding energies with water are -27.8 kJ mol-1 (2-NH2PYR) and -25.2 kJ mol-1 (2-NH2PYZ). The comparison with complexes involving nucleobases and one water molecule indicates that, in contrast with the interaction involving the carbonyl group, there is no correlation between the binding energies and the acidities and basicities of the sites involved in the interaction. The results are discussed in terms of marked angular differences of the hydrogen bonds forming the closed ring.