Observation of the hydration-dependent conformation of the (dG)20.(dG)20(dC)20 oligonucleotide triplex using FTIR spectroscopy.

The triple-helical oligonucleotide (dG)20.(dG)20(dC)20 was investigated using FTIR spectroscopy. Mid-infrared spectra were collected at nine relative humidities (RH) between 0% and 98%. The highest humidity spectrum agrees with the solution spectrum of a polynucleotide (dG)n.(dG)n(dC)n triplex [Quali, M., Letellier, R., Sun, J. S., Akhebat, A., Adnet, F., Liquier, J., & Taillandier, E. (1993) J. Am. Chem. Soc. 115, 4264-4270]. A dramatic transition in the vibrational state of the molecule has been observed between 88% and 92% RH. Theoretical predictions concerning the effects of hydration on a (dG).(dG)-(dC) oligonucleotide triplex [Laughton, C. A., & Neidle, S. (1992) Nucleic Acids Res. 20, 6535-6541; Mohan, V., Smith, P.E., & Pettitt, M.B. (1993) J. Am. Chem. Soc. 115, 9297-9298] have been considered and compared to our results. The infrared marker bands for the conformation of the glycosidic bond are absent below 92% RH, although dramatic hydration-dependent vibrational changes have been observed in the spectral regime traditionally associated with the glycosidic linkages. The effect of water in the Watson-Hoogsteen groove upon the vibrational state of the triplex has been observed for the first time. Hydration-induced changes in vibrational state have also been observed in the base residues, the phosphodiester backbone, and the furanose rings of the oligonucleotide sample.