Prediction of DNA far-IR absorption spectra based on normal mode analysis

We present a computational method which couples normal mode analysis in int ernal coordinates of a molecule with very far IR spectroscopy. The analytic al expression for the dependence of IR absorption on frequency incorporates frequencies and optical activities of each normal mode. In order to predic t far-IR spectra of a molecule we evaluate the optical activity of each nor mal mode. This optical activity is determined by the vibration amplitude of the dipole moment produced by a normal mode. We calculated normal modes of DNA double-helical fragments (dA)(12).(dT)(12) and (dA-dT)(6).(dA-dT)(6) a nd evaluated their optical activities. These were found to be very sensitiv e to the DNA basepair sequence. The positions of the resonance peaks in the calculated absorption spectrum of (dA)(12).(dT)(12) are in a good agreemen t with those obtained by Fourier transform IR spectroscopy (Powell JW et al . 1987 Phys Rev A 35: 3929-3939).