ANALYSIS OF [(DIEN)PD]2-SPECTROSCOPY( BINDING TO URACIL AND AZAURACILS BY PROTON NMR)

An analysis of the binding of [(dien)Pd]2+ to uracil, 6-azauracil and 5-azauracil has been performed by potentiometric pH titrations and pro ton NMR spectroscopy. Species of the type MBH predominate in the pH ra nge 2-11 for a 1:1 molar ration of [(dien)Pd]2+ and uracil. A doubly m etalated complex M2B is observed at a significant concentration for pH values above 6 and reaches a maximum at pH congruent-to 11. A similar macroscopic species distribution is also observed for the 1:1 [(dien) Pd]2+/6-azauracil system. N3 is the preferred binding site for both th e uracilate and 6-azauracilate anions in complexes of the type MBH; wh ereas an N1 coordinated species MBH is observed for uracil this is not the case for 6-azauracil. In contrast to 6-azauracil and its anions f or which no N6 coordinated species are registered in the H-1 NMR titra tions, N5 coordinated complexes of the type M2BH and MBH2 are observed as important species for the [(dien)Pd]2+/5-azauracil system. Satisfa ctory agreement is obtained between the potentiometric and proton NMR spectrometric formation constants beta for the three equilibrium syste ms studied.