APPLICATION OF A MULTIVARIATE CURVE RESOLUTION PROCEDURE FOR THE STUDY OF THE ACID-BASE AND COPPER(LI) COMPLEXATION EQUILIBRIA OF POLYCYTIDYLIC ACID

The acid-base properties and the copper(II)-complexing behaviour of th e polynucleotide polycytidylic acid (poly(C)) were studied by means of potentiometric, spectrophotometric and circular dichroism titrations in a working aqueous medium of 0.15 M ionic strength and at 37 degrees C. Spectrophotometric and circular dichroism data were treated with a multivariate curve resolution procedure that is successfully applied to the study of macromolecular systems, where polyfunctional, conforma tional and/or polyelectrolytic effects may be present. This procedure allows different sets of spectrometric titrations of the multi-equilib ria systems to be analyzed simultaneously. Three spectroscopically dif ferent species are detected for poly(C) in the pH range 3.1-7.0. Two o f them are forms with different protonation extent and different confo rmation, and the other is the unprotonated form of poly(C). One new sp ecies is detected in the presence of Cu(II) ion.