We report here the quantum chemical prediction of a new motif of the C-tetrad. The revealed H-bonding pattern of this tetrad conformer is different from that assumed on the base of the NMR experiment. The present study has predicted the small cavity pattern in which the four non-hydrogen-bonded amino protons point to the center of the tetrad. They are accessible to stack over the O6 atoms of the successive guanine tetrads. Both of the amino protons interact weakly with the N1 atom of the neighboring base. The stabilization energy of the C-tetrad is predicted to be 56.41 kcal/mol at the B3LYP/6-311G(d,p) level. (C) 2002 Elsevier Science B.V. All rights reserved.