APPLICATION OF A SELF-MODELING CURVE RESOLUTION APPROACH TO THE STUDYOF SOLVENT EFFECTS ON THE ACID-BASE AND COPPER(II)-COMPLEXING BEHAVIOR OF POLYURIDYLIC ACID

The solvent effect on the acid-base and complexation behavior of the h omopolynucleotide polyuridylic acid (poly(U)) has been studied by mean s of potentiometric and spectrometric titrations (circular dichroism a nd UV-VIS) in water and in 30 and 50% (v/v) dioxane-water media. The p otentiometric studies revealed the absence of polyelectrolytic effects in the acid-base equilibrium, and the spectrometric experiments detec ted only a random coil conformation associated with both the protonate d and deprotonated species. The common behavior observed in the three media seems to indicate the weakness of both intramolecular interactio ns, i.e., base stacking, and solute/solvent interactions, i.e., hydrog en-bonding, and consequently their small effect during the protonation process. Differences regarding the solubility of the deprotonated spe cies in the solvents used are due to the difficult stabilization of su ch a charged species in the low polar environment of the dioxane-water mixtures. Complexation has been exhaustively studied in aqueous media , and no conformational changes have been noticed in the only copper(I I)-poly(U) complex detected. The inclusion of the copper(II) ion in th e macromolecular skeleton of the polynucleotide does not contribute to an ordination of the structure, which remains as a random coil. No co mparison between this equilibrium in aqueous solution and in the hydro organic mixtures could be carried out since the limited pH range of th e soluble complex in those solvent mixtures prevented a rigorous quant itative monitoring of such a chemical process.