Vibrational analysis of phosphorothioate DNA .2. The POS group in the model compound dimethyl phosphorothioate [(CH3O)(2)(POS)](-)

The results of Raman and Infrared (IR) spectroscopic investigations on the vibrational modes of dimethyl phosphorothioate (DMPS) anion, [(CH3O)(2)(POS)](-), are reported. Ab initio calculations of the vibrational modes, the IR and Raman spectra and the interatomic force constants of DMPS were performed. A normal mode calculation was performed and the results were used to calculate the potential energy distribution for the vibrational modes. This analysis shows that in DMPS the P-S stretching mode has a frequency of about 630 cm(-1) and an angle bending mode involving the sulfur atom has a frequency of about 440 cm(-1). The proposed vibrational mode assignments will serve as marker bands in the conformational studies of phosphorothioate oligonucleotides which play a central role in the novel antisense therapeutic paradigm.