REACTIVITY OF NUCLEIC-ACIDS WITH OZONE - AN FT-IR MICROSPECTROSCOPY STUDY

Chemical changes were observed by Fourier transform microspectroscopy (FT-IR-M) in DNA and RNA samples treated with increasing amounts of oz one. The nucleobase reactivity and conformational changes in nucleic a cids were followed through the trend of certain spectroscopic paramete rs calculated from the spectra, The P-1 and P-2 parameters (calculated from the ratios of the optical densities of the bands at 1692 and 165 4 and at 1728 and 1654 cm(-1), respectively), involving base absorptio ns, are sensitive to the chemical action of ozone on covalent bonds of purinic and pirimidinic bases, The P-3 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 backbo ne of nucleic acids, We found that, as the amount of ozone increases, the P-1, P-2, and P-3 parameters increase for both the DNA and RNA sam ple spectra, but the curve trend and the concentration range that gave significant parameter changes were different for DNA and RNA, DNA spe ctra showed a sigmoidal increase in P-1 and P-2 parameters (C-1/2 = 1. 6 mg/mL, the concentration of ozone at which the parameters observed c hanged 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 P-3 vs. ozone concentration plot, Th e plots of P-1, P-2, and P-3 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 the se results, several hypotheses are suggested to explain the reaction m echanism of DNA and RNA nucleobases and the conformational changes in nucleic acids.