Reactivity of Nucleic Acids with Ozone: An FT-IR Microspectroscopy Study

Abstract

Chemical changes were observed by Fourier transform microspectroscopy (FT-IR-M) in DNA and RNA samples treated with increasing amounts of ozone. The nucleobase reactivity and conformational changes in nucleic acids were followed through the trend of certain spectroscopic parameters calculated from the spectra. The P₁ and P₂ parameters (calculated from the ratios of the optical densities of the bands at 1692 and 1654 and at 1728 and 1654 cm⁻¹, respectively), involving base absorptions, are sensitive to the chemical action of ozone on covalent bonds of purinic and pirimidinic bases. The P₃ parameter (calculated from the ratios of the optical densities of the bands at 1230 and 1090 cm⁻¹) is sensitive to conformational changes in the phosphate-ribose backbone of nucleic acids. We found that, as the amount of ozone increases, the P₁, P₂, and P₃ parameters increase for both the DNA and RNA sample spectra, but the curve trend and the concentration range that gave significant parameter changes were different for DNA and RNA. DNA spectra showed a sigmoidal increase in P₁ and P₂ parameters (C_1/2 = 1.6 mg/mL, the concentration of ozone at which the parameters observed changed by 50%), a plateau between 2 and 4.5 mg/mL of ozone, and a slow linear increase for ozone concentrations >5 mg/mL. Instead, a C_1/2 = 2.5 mg/mL was evaluated from the P₃ vs. ozone concentration plot. The plots of P₁, P₂, and P₃ parameters calculated from the RNA sample spectra vs. ozone concentration showed a saturation-shape curve that reached its maximum value between 0 and 1.9 mg/mL. On the basis of these results, several hypotheses are suggested to explain the reaction mechanism of DNA and RNA nucleobases and the conformational changes in nucleic acids.