SEQUENCE DEPENDENCE OF LOW-FREQUENCY RAMAN-ACTIVE MODES IN NUCLEIC-ACIDS

We have measured the low-frequency (< 200 cm-1) Raman activity of dehydrated fibers and films of polynucleotides and random-sequenced nucleic acids. The spectra exhibit a pronounced, unresolved band in the range 10-150 cm-1. A nonlinear least-squares algorithm optimally fits the spectra from all samples with three low-frequency modes in the range 25-100 cm-1 and a fourth mode near 200 cm-1. A mode near 25 cm-1 is sequence independent, but does shift to marginally higher frequency in RNA. The mode frequencies and oscillator strengths of two modes in the range 35-100 cm-1 exhibit sequence dependence.