The infrared and Raman spectra of the duplex of d(GGTATACC) in the crystal show bands due to both the A-form and the B-form of DNA

The deoxyoligonucleotide, d(GGTATACC), forms a duplex structure that crystallizes in the DNA A form. This has been shown by both X-ray diffraction studies and Raman spectroscopy (1,2). The presence of the DNA B form has been reported using diffuse X-ray scattering from a crystal of the closely related sequence d(GGBrUABrUACC)(3). In this paper the infrared spectrum of the d(GGTATACC) crystal is presented and curve resolution of both the Raman and IR spectra have been carried out. The percentage of A and B forms have been estimated. The %B form in the crystal has been estimated from the IR spectra to be about 15% and from Raman to be about 20%. Moreover the IR spectrum of the A conformation in the crystal is slightly different from the IR spectrum of the A conformation in polynucleotide fibers in particular in the region of the phosphate stretching vibrations and of the in-plane double bond vibrations of the bases. We show that it is feasible to obtain IR as well as Raman spectra of small crystals of oligonucleotides and that this is a good method of identifying all of the different conformations that may be in the crystal.