Infrared spectroscopy on poly(dG)-poly(dC) DNA at low hydration

Infrared absorption measurements have been made on dry samples of poly(dG)-poly(dC) DNA at various relative humidity and temperatures. The water content, controlled by the relative humidity, reduces as temperature increases and reaches a very low value of similar to 0.1 wpn above 120 degrees C. This minimum water content is maintained when the samples are brought back to room temperature as long as they are kept at the relative humidity of similar to 0%. The molecular vibrations, which characterize the backbone structure as well as the base stacking and pairing, indicate that our samples maintain an A-form double helical structure at all the values of water content. The disorder in the base stacking is observed as the result of the decrease of the water content. Additionally the denaturation appears at high temperatures above 100 degrees C, which reversibly disappears with decreasing temperature.