Analysis of uracil hydration by means of vibrational spectroscopy and density functional calculations

Interaction of water molecules (up to seven) with uracil (RNA base) through the first hydration shell has been analysed by means of density functional theory (DFT) calculations at the B3LYP/6-31G(*) level. Water molecules in uracil + 2H(2)O and uracil + 4H(2)O complexes interact with adjacent N-H and C double bondO chemical groups of the base. In addition to these groups, water molecules are also H-bonded to the uracil C-H groups in the uracil + 7H(2)O complex. It has been shown that the formation of water dimer and water trimer around uracil is necessary to complete its first hydration shell. Harmonic vibrational calculations have been performed after full geometry optimisation of each compound. A discussion has then been undertaken on the vibrational analysis of uracil in going from gas phase to solution state on the basis of available observed vibrational spectra and those calculated for isolated uracil and uracil + nH(2)O complexes. (C) 2001 Elsevier Science B.V. All rights reserved.