Hydration of single-stranded DNAs (oligonucleotides) of thymine (dT(10)) and adenine (dA(10)) in heavy water has been investigated using infrared absorption spectroscopy in the geometry of multiple internal reflection. Comparison of infrared absorption data with results of ab initio cluster calculation clearly indicates that water molecules are bound to the C=O and N-H bonds of the thymine base, giving rise to a red-shift of the C=O stretching vibration modes, and that the water molecule is site-specifically bound to the thymine base. We find that hydration induces a blue-shift of the ring deformation mode of the adenine base. (c) 2007 Elsevier B.V. All rights reserved.