A theoretical study on H-bonded complexes of thiouracil with leucine

The structure and stability in H-bonded complexes formed from interaction betweenthiouracil (T) and ieucine(L) have been investigated using B3LYP method with 6-311++G** basissets. With tree preferential interaction sites in the vicinity of the tiouracil, and two sites in thevicinity of the leucine six cyclic complexes (TL1-6) with two intermolecular hydrogen bonds(S)OT…H-O(N)L and OL…H-N(O)T were found on the potential energy surface. Six HB complexeshave electronic interaction energies (IEs) in the range of -57.534 to-24.937 kJ/mol that show thosemonomers are stabled by hydrogen bonding formation. The most stable complex is formed via NHbond of T with CO group of L and NH bond of L with CS group of T. The topological properties ofthe electron density distributions for intermolecular bridges have been analyzed in terms of theBader theory of atoms in molecules (AIM). Natural population analysis data, the electron densityand Laplacian properties have been used to evaluate the hydrogen bonding interactions. NBO andAIM analyses confirm that the charge transfer takes place from sulfur (oxygen) lone pair to s*O(N)-H antibond. Furthermore, calculated 1H NMR chemical shifts (δH) showed that the strengthening ofhydrogen bond causes 1H chemical shift of H moves to down fields.

کلیدواژه ها:

thiouracil ، leucine ، hydrogen bond ، AIM ، NBO