Density functional study of various thiouracil tetrads

In this paper the substituent effects caused by thiouracil (TU) on uracil tetrad have been investigated. The results of geometries, energies, frequencies and electronic structures have been presented. The outcomes show that the tetrads become more and more unstable as from U4 to 24TU4 through 2TU4 and 4TU4 (BSSE corrected binding energies), at the same time, both the vertical electron affinity and the adiabatic electron affinity increase as from U4 to 24TU4, which indicates that it turns to be easier and easier to inject an electron on the tetrad as from U4 to 24TU4. The stabilization energies and N3-H3 harmonic frequencies of U4 and 2TU4 are similar, while those of 4TU4 and 24TU4 are alike. The HOMO orbital of 2TU4 is different from U4 while 4TU4 and 24TU4 have similar constituents for both HOMO and LUMO orbitals.