RNA-ascorbate interaction.

Ascorbic acid and divalent iron salts have been widely used to investigate the effects of reactive oxygen species in different biological targets such as nucleic acids, proteins and lipids. This study was designed to examine the interaction of yeast RNA with vitamin C in aqueous solution at physiological pH with drug/RNA(P)(P=phosphate) molar ratios of r=1/80, 1/40, 1/20, 1/10, 1/4 and 1/2. Absorption spectra and Fourier transform infrared (FTIR) difference spectroscopy were used to determine the ascorbate binding mode, binding constant, sequence selectivity and RNA secondary structure in aqueous solution. Spectroscopic evidence showed that at low drug concentration (r=1/80 and 1/40), no major ascorbate-RNA interaction occurs, while at higher drug concentrations (r>1/40), a major drug-RNA complexation was observed through both G-C and A-U base pairs and the backbone phosphate groups with k=31.80 M(-1). Evidence for this comes from large perturbations of the G-C vibrations at 1698 and 1488 cm(-1) and the A-U bands at 1654 and 1608 cm(-1) as well as the phosphate antisymmetric stretch at 1244 cm(-1). At r>1/10, minor structural changes occur for the ribose-phosphate backbone geometry with RNA remaining in the A-family structure. The drug distributions around double helix were about 55% with G-C, 33% A-U and 12% with PO2 groups. A comparison between ascorbate-RNA and ascorbate-DNA complexes showed minor differences. The ascorbate binding (H-bonding) is via anion CO and OH groups.