Resumen de Stability constants of metal ion complexes formed with N3-deprotonated uridine in aqueous solution

Bernd Knobloch, Carla P. Da Costa, Wolfgang Linert, Helmut Sigel

• The acidity constant for the deprotonation of the (N3)H site of uridine (Urd) and the stability constants of the M(Urd–H)+ complexes with the metal ions M2+=Mg2+, Ca2+, Mn2+, Zn2+ or Cd2+ have been determined by potentiometric pH titrations in aqueous solution at 25 °C and I=0.1 M (NaNO3). The stability constant of the Pb(Urd–H)+ complex could not be measured due to the hydrolysis of Pb(aq)2+. It is shown that previously determined and compiled stability constants are far too large; the reason being most likely the neglect of M(aq)2+ hydrolysis, at least in the cases of Mn2+, Zn2+ and Cd2+. Because of the low stability of the alkaline earth ion complexes, it is suggested that in these instances outersphere species are formed which most likely also involve the C2 and/or C4 carbonyl oxygens of the uracil residue.