| Abstract: | We have measured the ir absorption of 5′CMP, 5′IMP, and poly(I)·poly(C) from ～25 to ～500 cm?1. From a comparison of the data with the previously measured absorption of the corresponding nucleosides and bases we can identify several “lines” associated with the deformation of the ribose ring. Out-of-plane deformation of the bases contributes strongly to vibrations near 200 cm?1. The same ribose vibrations observed in the nucleotides are found in poly(I)·poly(C). They sharpen with increasing water absorption. A study of the spectra of poly(I)·poly(C) as a function of the adsorbed water indicates that water does not contribute in a purely additive fashion to the polynucleotide spectrum but depends on the conformation of the helix. However, the only spectral feature that shifts drastically with conformation is near 45 cm?1. Measurements at cryogenic temperatures indicate some sharpening of the spectrum of poly(I)·poly(C). Instead, no sharpening is observed in the spectrum of the nucleotides. Shear degradation of poly(I)·poly(C) produces significant spectral changes in the 200-cm?1 region and sharpening of the features assigned to the low-frequency ribose-ring vibrations. |
