VIBRATIONAL ANALYSIS OF PHOSPHOROTHIOATE DNA .2. THE POS GROUP IN THEMODEL-COMPOUND DIMETHYL PHOSPHOROTHIOATE [(CH3O)(2)(POS)](-)

The results of Raman and Infrared (IR) spectroscopic investigations on the vibrational modes of dimethyl phosphorothioate (DMPS) anion, [(CH 3O)(2)(POS)](-), are reported. Ab initio calculations of the vibration al modes, the IR and Raman spectra and the interatomic force constants of DMPS were performed. A normal mode calculation was performed and t he results were used to calculate the potential energy distribution fo r the vibrational modes. This analysis shows that in DMPS the P-S stre tching mode has a frequency of about 630 cm(-1) and an angle bending m ode involving the sulfur atom has a frequency of about 440 cm(-1). The proposed vibrational mode assignments will serve as marker bands in t he conformational studies of phosphorothioate oligonucleotides which p lay a central role in the novel antisense therapeutic paradigm.