title: Spectrophotometric determination of the pK values for dissociation of the sugar hydroxyls in pyrimidine arabinonucleosides.
abstract: Spectrophotometric titration in the ultraviolet has been employed to determine the pK values for dissociation of the sugar hydroxyls in pyrimidine arabinonucleosides and some of their O'-methyl and O'-ethyl derivatives. The order of dissociation of the sugar hydroxyls in the arabinofuranose ring was 2'-OH greater than 3'-OH greater than 5'-OH. The higher acidity (lower pK) of the 2'-OH was interpreted in terms of formation of an intramolecular hydrogen bond of the form 5'-OH....2'-O(--) and the accompanying changes in conformation of the arabinose ring. The various factors affecting the dissociation of specific hydroxyls in some of the O'-alkyl derivatives are discussed in relation to steric, conformational and other effects.
mesh_terms: D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives; D001089:Arabinose; D011741:Pyrimidine Nucleosides; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011741:Pyrimidine Nucleosides; D001086:Arabinofuranosyluracil; D001089:Arabinose