The structures of the self-complementary decamer duplexes, $d(ACGTATACGT)_2$ (TATA-duplex) and $d(ACGTTAACGT)_2$, (TTAA-duplex) has been obtained in solution by proton NMR spectroscopy and restrained molecular dynamics. The duplexes are essentially B-type, with distortions apparent at the TATA and TTAA steps. Theses distortions and their effects on dynamics have been investigated by the measurement of imino proton exchange time of the base-pairs. The unusual opening kinetics of central A T base-pairs could be correlated to the abnormal structural properties of the corresponding sequences.