ABSTRACT
The pyrimidine nucleosides include cytidine, thymidine, and uridine. Of these, cytidine and thymidine are the constituents of the DNA strand and cytidine and uridine are part of the RNA strand. Of the three nucleosides mentioned, cytidine is the most thoroughly studied. Since electron density is delocalized over the entire pyrimidine ring, it is difficult to predict as to which site will be the binding site for the metal complex. However, the principal site of coordination of cytidine to a metal ion is mostly the heterocyclic nitrogen atom N(3). Thymidine and uridine are weaker donors than cytidine. The nucleosides exist in the keto form. Potentiometry is a useful technique for the determination of the association constants of the nucleosides with a proton or a metal ion. Most of the investigations covered in the chapter deal with potentiometry where the method was used to determine the composition of a binary or a ternary complex with the nucleosides and their corresponding stability constants.
